WINTER, SECRETARY OF THE NAVY, et al. v. NATU- RAL RESOURCES DEFENSE COUNCIL, INC., et al.

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Syllabus
WINTER, SECRETARY OF THE NAVY, et al. v. NATU-
RAL RESOURCES DEFENSE COUNCIL, INC., et al.
certiorari to the united states court of appeals for
the ninth circuit
No. 07–1239. Argued October 8, 2008—Decided November 12, 2008
Antisubmarine warfare is one of the Navy’s highest priorities. The
Navy’s fleet faces a significant threat from modern diesel-electric sub
marines, which are extremely difficult to detect and track because they
can operate almost silently. The most effective tool for identifying sub
merged diesel-electric submarines is active sonar, which emits pulses of
sound underwater and then receives the acoustic waves that echo off
the target. Active sonar is a complex technology, and sonar operators
must undergo extensive training to become proficient in its use.
This case concerns the Navy’s use of “mid-frequency active” (MFA)
sonar during integrated training exercises in the waters off southern
California (SOCAL). In these exercises, ships, submarines, and air
craft train together as members of a “strike group.” Due to the impor
tance of antisubmarine warfare, a strike group may not be certified for
deployment until it demonstrates proficiency in the use of active sonar
to detect, track, and neutralize enemy submarines.
The SOCAL waters contain at least 37 species of marine mammals.
The plaintiffs—groups and individuals devoted to the protection of ma
rine mammals and ocean habitats—assert that MFA sonar causes seri
ous injuries to these animals. The Navy disputes that claim, noting
that MFA sonar training in SOCAL waters has been conducted for 40
years without a single documented sonar-related injury to any marine
mammal. Plaintiffs sued the Navy, seeking declaratory and injunctive
relief on the grounds that the training exercises violated the National
Environmental Policy Act of 1969 (NEPA) and other federal laws;
in particular, plaintiffs contend that the Navy should have prepared
an environmental impact statement (EIS) before conducting the latest
round of SOCAL exercises.
The District Court entered a preliminary injunction prohibiting the
Navy from using MFA sonar during its training exercises. The Court
of Appeals held that this injunction was overbroad and remanded to the
District Court for a narrower remedy. The District Court then entered
another preliminary injunction, imposing six restrictions on the Navy’s
use of sonar during its SOCAL training exercises. As relevant to this
case, the injunction required the Navy to shut down MFA sonar when

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a marine mammal was spotted within 2,200 yards of a vessel, and to
power down sonar by 6 decibels during conditions known as “surface
ducting.”
The Navy then sought relief from the Executive Branch. The Coun
cil on Environmental Quality (CEQ) authorized the Navy to implement
“alternative arrangements” to NEPA compliance in light of “emergency
circumstances.” The CEQ allowed the Navy to continue its training
exercises under voluntary mitigation procedures that the Navy had pre
viously adopted.
The Navy moved to vacate the District Court’s preliminary injunction
in light of the CEQ’s actions. The District Court refused to do so, and
the Court of Appeals affirmed. The Court of Appeals held that there
was a serious question whether the CEQ’s interpretation of the “emer
gency circumstances” regulation was lawful, that plaintiffs had carried
their burden of establishing a “possibility” of irreparable injury, and
that the preliminary injunction was appropriate because the balance of
hardships and consideration of the public interest favored the plaintiffs.
The Court of Appeals emphasized that any negative impact of the in
junction on the Navy’s training exercises was “speculative,” and deter
mined that (1) the 2,200-yard shutdown zone was unlikely to affect naval
operations, because MFA sonar systems are often shut down during
training exercises; and (2) the power-down requirement during surface
ducting conditions was not unreasonable, because such conditions are
rare and the Navy has previously certified strike groups not trained
under these conditions.
Held: The preliminary injunction is vacated to the extent challenged by
the Navy. The balance of equities and the public interest—which were
barely addressed by the District Court—tip strongly in favor of the
Navy. The Navy’s need to conduct realistic training with active sonar
to respond to the threat posed by enemy submarines plainly outweighs
the interests advanced by the plaintiffs. Pp. 20–33.
(a) The lower courts held that when a plaintiff demonstrates a strong
likelihood of success on the merits, a preliminary injunction may be
entered based only on a “possibility” of irreparable harm. The “possi
bility” standard is too lenient. This Court’s frequently reiterated
standard requires plaintiffs seeking preliminary relief to demonstrate
that irreparable injury is likely in the absence of an injunction.
Even if plaintiffs have demonstrated a likelihood of irreparable injury,
such injury is outweighed by the public interest and the Navy’s interest
in effective, realistic training of its sailors. For the same reason, it is
unnecessary to address the lower courts’ holding that plaintiffs have
established a likelihood of success on the merits. Pp. 20–24.

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(b) A preliminary injunction is an extraordinary remedy never
awarded as of right. In each case, courts must balance the competing
claims of injury and consider the effect of granting or withholding the
requested relief, paying particular regard to the public consequences.
Weinberger v. Romero-Barcelo, 456 U. S. 305, 312. Military interests
do not always trump other considerations, and the Court has not held
that they do, but courts must give deference to the professional judg
ment of military authorities concerning the relative importance of a par
ticular military interest. Goldman v. Weinberger, 475 U. S. 503, 507.
Here, the record contains declarations from some of the Navy’s most
senior officers, all of whom underscored the threat posed by enemy sub
marines and the need for extensive sonar training to counter this threat.
Those officers emphasized that realistic training cannot be accomplished
under the two challenged restrictions imposed by the District Court—
the 2,200-yard shutdown zone and the power-down requirement during
surface ducting conditions. The use of MFA sonar under realistic con
ditions during training exercises is clearly of the utmost importance to
the Navy and the Nation. The Court does not question the importance
of plaintiffs’ ecological, scientific, and recreational interests, but it con
cludes that the balance of equities and consideration of the overall public
interest tip strongly in favor of the Navy. The determination of where
the public interest lies in this case does not strike the Court as a close
question. Pp. 24–26.
(c) The lower courts’ justifications for entering the preliminary in
junction are not persuasive. Pp. 26–31.
(1) The District Court did not give serious consideration to the bal
ance of equities and the public interest. The Court of Appeals did con
sider these factors and conclude that the Navy’s concerns about the
preliminary injunction were “speculative.” But that is almost always
the case when a plaintiff seeks injunctive relief to alter a defendant’s
conduct. The lower courts failed properly to defer to senior Navy offi
cers’ specific, predictive judgments about how the preliminary injunc
tion would reduce the effectiveness of the Navy’s SOCAL training exer
cises. Pp. 26–27.
(2) The District Court abused its discretion by requiring the Navy
to shut down MFA sonar when a marine mammal is spotted within 2,200
yards of a sonar-emitting vessel. The Court of Appeals concluded that
the zone would not be overly burdensome because marine mammal
sightings during training exercises are relatively rare. But regardless
of the frequency of such sightings, the injunction will increase the radius
of the shutdown zone from 200 to 2,200 yards, which expands its surface
area by a factor of over 100. Moreover, because training scenarios can
take several days to develop, each additional shutdown can result in

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10 WINTER v. NATURAL RESOURCES DEFENSE
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the loss of several days’ worth of training. The Court of Appeals also
concluded that the shutdown zone would not be overly burdensome be
cause the Navy had shut down MFA sonar several times during prior
exercises when marine mammals were spotted well beyond the Navy’s
self-imposed 200-yard zone. But the court ignored undisputed evidence
that these voluntary shutdowns only occurred during tactically insig
nificant times. Pp. 27–29.
(3) The District Court also abused its discretion by requiring the
Navy to power down MFA sonar by 6 decibels during significant surface
ducting conditions. When surface ducting occurs, active sonar becomes
more useful near the surface, but less effective at greater depths.
Diesel-electric submariners are trained to take advantage of these dis
tortions to avoid being detected by sonar. The Court of Appeals con
cluded that the power-down requirement was reasonable because sur
face ducting occurs relatively rarely, and the Navy has previously
certified strike groups that did not train under such conditions. This
reasoning is backwards. Given that surface ducting is both rare and
unpredictable, it is especially important for the Navy to be able to train
under these conditions when they occur. Pp. 29–30.
(4) The Navy has previously taken voluntary measures to address
concerns about marine mammals, and has chosen not to challenge four
other restrictions imposed by the District Court in this case. But that
hardly means that other, more intrusive restrictions pose no threat to
preparedness for war. The Court of Appeals noted that the Navy could
return to the District Court to seek modification of the preliminary in
junction if it actually resulted in an inability to train. The Navy is not
required to wait until it is unable to train sufficient forces for national
defense before seeking dissolution of the preliminary injunction. By
then it may be too late. Pp. 30–31.
(d) This Court does not address the underlying merits of plaintiffs’
claims, but the foregoing analysis makes clear that it would also be an
abuse of discretion to enter a permanent injunction along the same lines
as the preliminary injunction. Plaintiffs’ ultimate legal claim is that
the Navy must prepare an EIS, not that it must cease sonar training.
There is accordingly no basis for enjoining such training pending prepa
ration of an EIS—if one is determined to be required—when doing so
is credibly alleged to pose a serious threat to national security. There
are many other remedial tools available, including declaratory relief or
an injunction specifically tailored to preparation of an EIS, that do not
carry such dire consequences. Pp. 31–33.
518 F. 3d 658, reversed; preliminary injunction vacated in part.
Roberts, C. J., delivered the opinion of the Court, in which Scalia,
Kennedy, Thomas, and Alito, JJ., joined. Breyer, J., filed an opinion

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concurring in part and dissenting in part, in which Stevens, J., joined as
to Part I, post, p. 34. Ginsburg, J., filed a dissenting opinion, in which
Souter, J., joined, post, p. 43.
Solicitor General Garre argued the cause for petitioners.
With him on the briefs were Assistant Attorney General
Tenpas, Deputy Solicitor General Kneedler, Deputy Assist
ant Attorney General Nelson, Anthony A. Yang, Andrew C.
Mergen, Michael R. Eitel, Luther L. Hajek, Allen M. Brab
ender, Daniel J. Dell’Orto, Thomas N. Ledvina, J. Page Tur
ney, Jane C. Luxton, Mary Beth Ward, Joel La Bissonniere,
and Edward A. Boling.
Richard B. Kendall argued the cause for respondents.
With him on the brief for respondent environmentalists were
Robert N. Klieger, Gregory A. Fayer, Joel R. Reynolds, Cara
A. Horowitz, and Stephen Zak Smith.
Edmund G. Brown, Jr., Attorney General of California,
filed a brief for respondent California Coastal Commission.
With him on the brief were Jamee Jordan Patterson, Super
vising Deputy Attorney General, J. Matthew Rodriquez,
Chief Assistant Attorney General, Manuel M. Medeiros,
Solicitor General, and Gordon Burns, Deputy Solicitor
General.*
*Briefs of amici curiae urging reversal were filed for the Navy League
of the United States—Honolulu Council et al. by Robert H. Thomas, Mark
M. Murakami, Theodore G. Meeker, and Michael A. Lilly; for the Pacific
Legal Foundation by M. Reed Hopper and Steven Geoffrey Gieseler; and
for the Washington Legal Foundation et al. by Andrew G. McBride, Dan
iel J. Popeo, and Paul D. Kamenar.
Briefs of amici curiae urging affirmance were filed for the Ecological
Society of America by Peter E. Perkowski; for California Assembly Mem
ber Julia Brownley et al. by Stephen B. Kinnaird, Peter H. Weiner, Paul
W. Cane, Jr., and Sean D. Unger; and for Michael C. Small et al. by
Mr. Small, pro se, Jonathan D. Varat, and Edward P. Lazarus.
Briefs of amici curiae were filed for the California Forestry Association
et al. by Thomas R. Lundquist, J. Michael Klise, Michele Dias, William
R. Murray, Douglas T. Nelson, Duane J. Desiderio, and Thomas J. Ward;
and for Defenders of Wildlife et al. by Eric R. Glitzenstein.

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12 WINTER v. NATURAL RESOURCES DEFENSE
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Opinion of the Court
Chief Justice Roberts delivered the opinion of the
Court.
“To be prepared for war is one of the most effectual means
of preserving peace.” 1 Messages and Papers of the Presi
dents 57 (J. Richardson comp. 1897). So said George Wash
ington in his first Annual Address to Congress, 218 years
ago. One of the most important ways the Navy prepares for
war is through integrated training exercises at sea. These
exercises include training in the use of modern sonar to de
tect and track enemy submarines, something the Navy has
done for the past 40 years. The plaintiffs, respondents here,
complained that the Navy’s sonar-training program harmed
marine mammals, and that the Navy should have prepared
an environmental impact statement before commencing its
latest round of training exercises. The Court of Appeals up
held a preliminary injunction imposing restrictions on the
Navy’s sonar training, even though that court acknowledged
that “the record contains no evidence that marine mammals
have been harmed” by the Navy’s exercises. 518 F. 3d 658,
696 (CA9 2008).
The Court of Appeals was wrong, and its decision is
reversed.
I
The Navy deploys its forces in “strike groups,” which are
groups of surface ships, submarines, and aircraft centered
around either an aircraft carrier or an amphibious assault
ship. App. to Pet. for Cert. 316a–317a (Pet. App.). Seam
less coordination among strike-group assets is critical. Be
fore deploying a strike group, the Navy requires extensive
integrated training in analysis and prioritization of threats,
execution of military missions, and maintenance of force pro
tection. App. 110–111.
Antisubmarine warfare is currently the Pacific Fleet’s top
war-fighting priority. Pet. App. 270a–271a. Modern diesel
electric submarines pose a significant threat to Navy vessels
because they can operate almost silently, making them ex

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tremely difficult to detect and track. Potential adversaries
of the United States possess at least 300 of these subma
rines. App. 571.
The most effective technology for identifying submerged
diesel-electric submarines within their torpedo range is ac
tive sonar, which involves emitting pulses of sound underwa
ter and then receiving the acoustic waves that echo off the
target. Pet. App. 266a–267a, 274a. Active sonar is a par
ticularly useful tool because it provides both the bearing and
the distance of target submarines; it is also sensitive enough
to allow the Navy to track enemy submarines that are qui
eter than the surrounding marine environment.1 This case
concerns the Navy’s use of “mid-frequency active” (MFA)
sonar, which transmits sound waves at frequencies between
1 kHz and 10 kHz.
Not surprisingly, MFA sonar is a complex technology, and
sonar operators must undergo extensive training to become
proficient in its use. Sonar reception can be affected by
countless different factors, including the time of day, water
density, salinity, currents, weather conditions, and the con
tours of the sea floor. Id., at 278a–279a. When working as
part of a strike group, sonar operators must be able to coor
dinate with other Navy ships and planes while avoiding in
terference. The Navy conducts regular training exercises
under realistic conditions to ensure that sonar operators are
thoroughly skilled in its use in a variety of situations.
The waters off the coast of southern California (SOCAL)
are an ideal location for conducting integrated training exer
cises, as this is the only area on the west coast that is rela
tively close to land, air, and sea bases, as well as amphibious
1 In contrast, passive sonar “listens” for sound waves but does not intro
duce sound into the water. Passive sonar is not effective for tracking
diesel-electric submarines because those vessels can operate almost si
lently. Passive sonar also has a more limited range than active sonar, and
cannot identify the exact location of an enemy submarine. Pet. App.
266a–271a.

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landing areas. App. 141–142. At issue in this case are the
Composite Training Unit Exercises and the Joint Tactical
Force Exercises, in which individual naval units (ships, sub
marines, and aircraft) train together as members of a strike
group. A strike group cannot be certified for deployment
until it has successfully completed the integrated training
exercises, including a demonstration of its ability to operate
under simulated hostile conditions. Id., at 564–565. In
light of the threat posed by enemy submarines, all strike
groups must demonstrate proficiency in antisubmarine war
fare. Accordingly, the SOCAL exercises include extensive
training in detecting, tracking, and neutralizing enemy sub
marines. The use of MFA sonar during these exercises is
“mission-critical,” given that MFA sonar is the only proven
method of identifying submerged diesel-electric submarines
operating on battery power. Id., at 568–571.
Sharing the waters in the SOCAL operating area are at
least 37 species of marine mammals, including dolphins,
whales, and sea lions. The parties strongly dispute the ex
tent to which the Navy’s training activities will harm those
animals or disrupt their behavioral patterns. The Navy em
phasizes that it has used MFA sonar during training exer
cises in SOCAL for 40 years, without a single documented
sonar-related injury to any marine mammal. The Navy as
serts that, at most, MFA sonar may cause temporary hearing
loss or brief disruptions of marine mammals’ behavioral
patterns.
The plaintiffs are the Natural Resources Defense Council,
Inc., Jean-Michael Cousteau (an environmental enthusiast
and filmmaker), and several other groups devoted to the pro
tection of marine mammals and ocean habitats. They con
tend that MFA sonar can cause much more serious injuries
to marine mammals than the Navy acknowledges, including
permanent hearing loss, decompression sickness, and major
behavioral disruptions. According to the plaintiffs, several
mass strandings of marine mammals (outside of SOCAL)

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have been “associated” with the use of active sonar. They
argue that certain species of marine mammals—such as
beaked whales—are uniquely susceptible to injury from ac
tive sonar; these injuries would not necessarily be detected
by the Navy, given that beaked whales are “very deep di
vers” that spend little time at the surface.
II
The procedural history of this case is rather complicated.
The Marine Mammal Protection Act of 1972 (MMPA), 86
Stat. 1027, generally prohibits any individual from “taking”
a marine mammal, defined as harassing, hunting, capturing,
or killing it. 16 U. S. C. §§ 1362(13), 1372(a). The Secretary
of Defense may “exempt any action or category of actions”
from the MMPA if such actions are “necessary for national
defense.” § 1371(f)(1). In January 2007, the Deputy Secre
tary of Defense—acting for the Secretary—granted the
Navy a 2-year exemption from the MMPA for the training
exercises at issue in this case. Pet. App. 219a–220a. The
exemption was conditioned on the Navy adopting several
mitigation procedures, including: (1) training lookouts and of
ficers to watch for marine mammals; (2) requiring at least
five lookouts with binoculars on each vessel to watch for
anomalies on the water surface (including marine mammals);
(3) requiring aircraft and sonar operators to report detected
marine mammals in the vicinity of the training exercises;
(4) requiring reduction of active sonar transmission levels by
6 dB if a marine mammal is detected within 1,000 yards of
the bow of the vessel, or by 10 dB if detected within 500
yards; (5) requiring complete shutdown of active sonar trans
mission if a marine mammal is detected within 200 yards of
the vessel; (6) requiring active sonar to be operated at the
“lowest practicable level”; and (7) adopting coordination and
reporting procedures. Id., at 222a–230a.
The National Environmental Policy Act of 1969 (NEPA),
83 Stat. 852, requires federal agencies “to the fullest extent

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possible” to prepare an environmental impact statement
(EIS) for “every . . . major Federal actio[n] significantly af
fecting the quality of the human environment.” 42 U. S. C.
§ 4332(2)(C) (2000 ed.). An agency is not required to pre
pare a full EIS if it determines—based on a shorter envi
ronmental assessment (EA)—that the proposed action will
not have a significant impact on the environment. 40 CFR
§§ 1508.9(a), 1508.13 (2007).
In February 2007, the Navy issued an EA concluding that
the 14 SOCAL training exercises scheduled through January
2009 would not have a significant impact on the environment.
App. 226–227. The EA divided potential injury to marine
mammals into two categories: Level A harassment, defined
as the potential destruction or loss of biological tissue (i. e.,
physical injury), and Level B harassment, defined as tempo
rary injury or disruption of behavioral patterns such as mi
gration, feeding, surfacing, and breeding. Id., at 160–161.
The Navy’s computer models predicted that the SOCAL
training exercises would cause only eight Level A harass
ments of common dolphins each year, and that even these
injuries could be avoided through the Navy’s voluntary miti
gation measures, given that dolphins travel in large pods
easily located by Navy lookouts. Id., at 176–177, 183. The
EA also predicted 274 Level B harassments of beaked
whales per year, none of which would result in permanent
injury. Id., at 185–186. Beaked whales spend little time at
the surface, so the precise effect of active sonar on these
mammals is unclear. Erring on the side of caution, the
Navy classified all projected harassments of beaked whales
as Level A. Id., at 186, 223. In light of its conclusion that
the SOCAL training exercises would not have a significant
impact on the environment, the Navy determined that it was
unnecessary to prepare a full EIS. See 40 CFR § 1508.13.
Shortly after the Navy released its EA, the plaintiffs sued
the Navy, seeking declaratory and injunctive relief on the
grounds that the Navy’s SOCAL training exercises violated

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NEPA, the Endangered Species Act of 1973 (ESA), and the
Coastal Zone Management Act of 1972 (CZMA).2 The Dis
trict Court granted plaintiffs’ motion for a preliminary in
junction and prohibited the Navy from using MFA sonar dur
ing its remaining training exercises. The court held that
plaintiffs had “demonstrated a probability of success” on
their claims under NEPA and the CZMA. Pet. App. 207a,
215a. The court also determined that equitable relief was
appropriate because, under Ninth Circuit precedent, plain
tiffs had established at least a “ ‘possibility’ ” of irreparable
harm to the environment. Id., at 217a. Based on scientific
studies, declarations from experts, and other evidence in the
record, the District Court concluded that there was in fact a
“near certainty” of irreparable injury to the environment,
and that this injury outweighed any possible harm to the
Navy. Id., at 217a–218a.
The Navy filed an emergency appeal, and the Ninth Cir
cuit stayed the injunction pending appeal. 502 F. 3d 859,
865 (2007). After hearing oral argument, the Court of Ap
peals agreed with the District Court that preliminary injunc
tive relief was appropriate. The appellate court concluded,
however, that a blanket injunction prohibiting the Navy from
using MFA sonar in SOCAL was overbroad, and remanded
the case to the District Court “to narrow its injunction so as
to provide mitigation conditions under which the Navy may
conduct its training exercises.” 508 F. 3d 885, 887 (2007).
On remand, the District Court entered a new preliminary
injunction allowing the Navy to use MFA sonar only as long
as it implemented the following mitigation measures (in addi
tion to the measures the Navy had adopted pursuant to its
MMPA exemption): (1) imposing a 12 nautical mile “exclusion
2 The CZMA states that federal agencies taking actions “that affec[t]
any land or water use or natural resource of the coastal zone” shall carry
out these activities “in a manner which is consistent to the maximum ex
tent practicable with the enforceable policies of approved State manage
ment programs.” 16 U. S. C. § 1456(c)(1)(A).

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zone” from the coastline; (2) using lookouts to conduct addi
tional monitoring for marine mammals; (3) restricting the
use of “helicopter-dipping” sonar; (4) limiting the use of MFA
sonar in geographic “choke points”; (5) shutting down MFA
sonar when a marine mammal is spotted within 2,200 yards
of a vessel; and (6) powering down MFA sonar by 6 dB dur
ing significant surface ducting conditions, in which sound
travels further than it otherwise would due to temperature
differences in adjacent layers of water. 530 F. Supp. 2d
1110, 1118–1121 (CD Cal. 2008). The Navy filed a notice of
appeal, challenging only the last two restrictions.
The Navy then sought relief from the Executive Branch.
The President, pursuant to 16 U. S. C. § 1456(c)(1)(B), granted
the Navy an exempti on from the CZMA. Secti on
1456(c)(1)(B) permits such exemptions if the activity in ques
tion is “in the paramount interest of the United States.”
The President determined that continuation of the exercises
as limited by the Navy was “essential to national security.”
Pet. App. 232a. He concluded that compliance with the Dis
trict Court’s injunction would “undermine the Navy’s ability
to conduct realistic training exercises that are necessary to
ensure the combat effectiveness of . . . strike groups.” Ibid.
Simultaneously, the Council on Environmental Quality
(CEQ) authorized the Navy to implement “alternative ar
rangements” to NEPA compliance in light of “emergency
circumstances.” See 40 CFR § 1506.11.3 The CEQ de
termined that alternative arrangements were appropriate
because the District Court’s injunction “create[s] a signifi
cant and unreasonable risk that Strike Groups will not be
3 That provision states in full: “Where emergency circumstances make it
necessary to take an action with significant environmental impact without
observing the provisions of these regulations, the Federal agency taking
the action should consult with the Council about alternative arrangements.
Agencies and the Council will limit such arrangements to actions neces
sary to control the immediate impacts of the emergency. Other actions
remain subject to NEPA review.”

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able to train and be certified as fully mission capable.” Pet.
App. 238a. Under the alternative arrangements, the Navy
would be permitted to conduct its training exercises under
the mitigation procedures adopted in conjunction with the
exemption from the MMPA. The CEQ also imposed addi
tional notice, research, and reporting requirements.
In light of these actions, the Navy then moved to vacate
the District Court’s injunction with respect to the 2,200-yard
shutdown zone and the restrictions on training in surface
ducting conditions. The District Court refused to do so, 527
F. Supp. 2d 1216 (2008), and the Court of Appeals affirmed.
The Ninth Circuit held that there was a serious question
regarding whether the CEQ’s interpretation of the “emer
gency circumstances” regulation was lawful. Specifically,
the court questioned whether there was a true “emergency”
in this case, given that the Navy has been on notice of its
obligation to comply with NEPA from the moment it first
planned the SOCAL training exercises. 518 F. 3d, at 681.
The Court of Appeals concluded that the preliminary injunc
tion was entirely predictable in light of the parties’ litigation
history. Ibid. The court also held that plaintiffs had estab
lished a likelihood of success on their claim that the Navy
was required to prepare a full EIS for the SOCAL training
exercises. Id., at 693. The Ninth Circuit agreed with the
District Court’s holding that the Navy’s EA—which resulted
in a finding of no significant environmental impact—was
“cursory, unsupported by cited evidence, or unconvincing.”
Ibid.4
The Court of Appeals further determined that plaintiffs
had carried their burden of establishing a “possibility” of ir
reparable injury. Even under the Navy’s own figures, the
court concluded, the training exercises would cause 564 phys
ical injuries to marine mammals, as well as 170,000 disturb
4 The Ninth Circuit’s discussion of the plaintiffs’ likelihood of success
was limited to their NEPA claims. The court did not discuss claims under
the CZMA or ESA.

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ances of marine mammals’ behavior. Id., at 696. Lastly,
the Court of Appeals held that the balance of hardships and
consideration of the public interest weighed in favor of the
plaintiffs. The court emphasized that the negative impact
on the Navy’s training exercises was “speculative,” since the
Navy has never before operated under the procedures re
quired by the District Court. Id., at 698–699. In particu
lar, the court determined that: (1) The 2,200-yard shutdown
zone imposed by the District Court was unlikely to affect the
Navy’s operations, because the Navy often shuts down its
MFA sonar systems during the course of training exercises;
and (2) the power-down requirement during significant sur
face ducting conditions was not unreasonable because such
conditions are rare, and the Navy has previously certified
strike groups that had not trained under such conditions.
Id., at 699–702. The Ninth Circuit concluded that the Dis
trict Court’s preliminary injunction struck a proper balance
between the competing interests at stake.
We granted certiorari, 554 U. S. 916 (2008), and now re
verse and vacate the injunction.
III
A
A plaintiff seeking a preliminary injunction must establish
that he is likely to succeed on the merits, that he is likely to
suffer irreparable harm in the absence of preliminary relief,
that the balance of equities tips in his favor, and that an
injunction is in the public interest. See Munaf v. Geren, 553
U. S. 674, 689–690 (2008); Amoco Production Co. v. Gambell,
480 U. S. 531, 542 (1987); Weinberger v. Romero-Barcelo, 456
U. S. 305, 311–312 (1982).
The District Court and the Ninth Circuit concluded that
plaintiffs have shown a likelihood of success on the merits
of their NEPA claim. The Navy strongly disputes this de
termination, arguing that plaintiffs’ likelihood of success is
low because the CEQ reasonably concluded that “emergency

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circumstances” justified alternative arrangements to NEPA
compliance. 40 CFR § 1506.11. Plaintiffs’ briefs before
this Court barely discuss the ground relied upon by the
lower courts—that the plain meaning of “emergency circum
stances” does not encompass a court order that was “entirely
predictable” in light of the parties’ litigation history. 518
F. 3d, at 681. Instead, plaintiffs contend that the CEQ’s ac
tions violated the separation of powers by readjudicating a
factual issue already decided by an Article III court. More
over, they assert that the CEQ’s interpretations of NEPA
are not entitled to deference because the CEQ has not been
given statutory authority to conduct adjudications.
The District Court and the Ninth Circuit also held that
when a plaintiff demonstrates a strong likelihood of prevail
ing on the merits, a preliminary injunction may be entered
based only on a “possibility” of irreparable harm. Id., at
696–697; 530 F. Supp. 2d, at 1118 (quoting Faith Center
Church Evangelistic Ministries v. Glover, 480 F. 3d 891, 906
(CA9 2007); Earth Island Inst. v. United States Forest Serv.,
442 F. 3d 1147, 1159 (CA9 2006)). The lower courts held that
plaintiffs had met this standard because the scientific stud
ies, declarations, and other evidence in the record estab
lished to “a near certainty” that the Navy’s training exer
cises would cause irreparable harm to the environment. 530
F. Supp. 2d, at 1118.
The Navy challenges these holdings, arguing that plain
tiffs must demonstrate a likelihood of irreparable injury—
not just a possibility—in order to obtain preliminary relief.
On the facts of this case, the Navy contends that plaintiffs’
alleged injuries are too speculative to give rise to irreparable
injury, given that ever since the Navy’s training program
began 40 years ago, there has been no documented case of
sonar-related injury to marine mammals in SOCAL. And
even if MFA sonar does cause a limited number of injuries
to individual marine mammals, the Navy asserts that plain
tiffs have failed to offer evidence of species-level harm that

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would adversely affect their scientific, recreational, and eco
logical interests. For their part, plaintiffs assert that they
would prevail under any formulation of the irreparable in
jury standard, because the District Court found that they
had established a “near certainty” of irreparable harm.
We agree with the Navy that the Ninth Circuit’s “possi
bility” standard is too lenient. Our frequently reiterated
standard requires plaintiffs seeking preliminary relief to
demonstrate that irreparable injury is likely in the absence
of an injunction. Los Angeles v. Lyons, 461 U. S. 95, 103
(1983); Granny Goose Foods, Inc. v. Teamsters, 415 U. S. 423,
441 (1974); O’Shea v. Littleton, 414 U. S. 488, 502 (1974); see
also 11A C. Wright, A. Miller, & M. Kane, Federal Practice
and Procedure § 2948.1, p. 139 (2d ed. 1995) (hereinafter
Wright & Miller) (applicant must demonstrate that in the
absence of a preliminary injunction, “the applicant is likely
to suffer irreparable harm before a decision on the merits
can be rendered”); id., at 154–155 (“[A] preliminary injunc
tion will not be issued simply to prevent the possibility of
some remote future injury”). Issuing a preliminary injunc
tion based only on a possibility of irreparable harm is incon
sistent with our characterization of injunctive relief as an
extraordinary remedy that may only be awarded upon a clear
showing that the plaintiff is entitled to such relief. Mazurek
v. Armstrong, 520 U. S. 968, 972 (1997) (per curiam).
It is not clear that articulating the incorrect standard af
fected the Ninth Circuit’s analysis of irreparable harm. Al
though the court referred to the “possibility” standard, and
cited Circuit precedent along the same lines, it affirmed the
District Court’s conclusion that plaintiffs had established a
“ ‘near certainty’ ” of irreparable harm. 518 F. 3d, at 696–
697. At the same time, however, the nature of the District
Court’s conclusion is itself unclear. The District Court orig
inally found irreparable harm from sonar-training exercises
generally. But by the time of the District Court’s final
decision, the Navy challenged only two of six restrictions

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imposed by the court. See supra, at 17–19. The District
Court did not reconsider the likelihood of irreparable harm
in light of the four restrictions not challenged by the Navy.
This failure is significant in light of the District Court’s own
statement that the 12 nautical mile exclusion zone from the
coastline—one of the unchallenged mitigation restrictions—
“would bar the use of MFA sonar in a significant portion of
important marine mammal habitat.” 530 F. Supp. 2d, at
1119.
We also find it pertinent that this is not a case in which
the defendant is conducting a new type of activity with com
pletely unknown effects on the environment. When the
Government conducts an activity, “NEPA itself does not
mandate particular results.” Robertson v. Methow Valley
Citizens Council, 490 U. S. 332, 350 (1989). Instead, NEPA
imposes only procedural requirements to “ensur[e] that the
agency, in reaching its decision, will have available, and will
carefully consider, detailed information concerning signifi
cant environmental impacts.” Id., at 349. Part of the harm
NEPA attempts to prevent in requiring an EIS is that, with
out one, there may be little if any information about prospec
tive environmental harms and potential mitigating measures.
Here, in contrast, the plaintiffs are seeking to enjoin—or
substantially restrict—training exercises that have been
taking place in SOCAL for the last 40 years. And the latest
series of exercises were not approved until after the defend
ant took a “hard look at environmental consequences,” id.,
at 350 (quoting Kleppe v. Sierra Club, 427 U. S. 390, 410,
n. 21 (1976); internal quotation marks omitted), as evidenced
by the issuance of a detailed, 293-page EA.
As explained in the next section, even if plaintiffs have
shown irreparable injury from the Navy’s training exercises,
any such injury is outweighed by the public interest and the
Navy’s interest in effective, realistic training of its sailors.
A proper consideration of these factors alone requires denial
of the requested injunctive relief. For the same reason, we

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do not address the lower courts’ holding that plaintiffs have
also established a likelihood of success on the merits.
B
A preliminary injunction is an extraordinary remedy
never awarded as of right. Munaf, 553 U. S., at 689–690.
In each case, courts “must balance the competing claims of
injury and must consider the effect on each party of the
granting or withholding of the requested relief.” Amoco
Production Co., 480 U. S., at 542. “In exercising their sound
discretion, courts of equity should pay particular regard for
the public consequences in employing the extraordinary rem
edy of injunction.” Romero-Barcelo, 456 U. S., at 312; see
also Railroad Comm’n of Tex. v. Pullman Co., 312 U. S. 496,
500 (1941). In this case, the District Court and the Ninth
Circuit significantly understated the burden the preliminary
injunction would impose on the Navy’s ability to conduct
realistic training exercises, and the injunction’s consequent
adverse impact on the public interest in national defense.
This case involves “complex, subtle, and professional deci
sions as to the composition, training, equipping, and control
of a military force,” which are “essentially professional mili
tary judgments.” Gilligan v. Morgan, 413 U. S. 1, 10 (1973).
We “give great deference to the professional judgment of
military authorities concerning the relative importance of a
particular military interest.” Goldman v. Weinberger, 475
U. S. 503, 507 (1986). As the Court emphasized just last
Term, “neither the Members of this Court nor most federal
judges begin the day with briefings that may describe new
and serious threats to our Nation and its people.” Boume
diene v. Bush, 553 U. S. 723, 797 (2008).
Here, the record contains declarations from some of the
Navy’s most senior officers, all of whom underscored the
threat posed by enemy submarines and the need for exten
sive sonar training to counter this threat. Admiral Gary

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Roughead—the Chief of Naval Operations—stated that dur
ing training exercises:
“It is important to stress the ship crews in all dimen
sions of warfare simultaneously. If one of these train
ing elements were impacted—for example, if effective
sonar training were not possible—the training value of
the other elements would also be degraded . . . .” Pet.
App. 342a.
Captain Martin May—the Third Fleet’s Assistant Chief of
Staff for Training and Readiness—emphasized that the use
of MFA sonar is “mission-critical.” App. 570–571. He de
scribed the ability to operate MFA sonar as a “highly perish
able skill” that must be repeatedly practiced under realistic
conditions. Id., at 577. During training exercises, MFA
sonar operators learn how to avoid sound-reducing “clutter”
from ocean floor topography and environmental conditions;
they also learn how to avoid interference and how to coordi
nate their efforts with other sonar operators in the strike
group. Id., at 574. Several Navy officers emphasized that
realistic training cannot be accomplished under the two chal
lenged restrictions imposed by the District Court—the
2,200-yard shutdown zone and the requirement that the
Navy power down its sonar systems during significant sur
face ducting conditions. See, e. g., Pet. App. 333a (powering
down in presence of surface ducting “unreasonably prevent[s]
realistic training”); id., at 356a (shutdown zone would “result
in a significant, adverse impact to realistic training”). We
accept these officers’ assertions that the use of MFA sonar
under realistic conditions during training exercises is of the
utmost importance to the Navy and the Nation.
These interests must be weighed against the possible harm
to the ecological, scientific, and recreational interests that
are legitimately before this Court. Plaintiffs have submit
ted declarations asserting that they take whale watching
trips, observe marine mammals underwater, conduct scien

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tific research on marine mammals, and photograph these ani
mals in their natural habitats. Plaintiffs contend that the
Navy’s use of MFA sonar will injure marine mammals or
alter their behavioral patterns, impairing plaintiffs’ ability
to study and observe the animals.
While we do not question the seriousness of these inter
ests, we conclude that the balance of equities and consider
ation of the overall public interest in this case tip strongly
in favor of the Navy. For the plaintiffs, the most serious
possible injury would be harm to an unknown number of the
marine mammals that they study and observe. In contrast,
forcing the Navy to deploy an inadequately trained antisub
marine force jeopardizes the safety of the fleet. Active
sonar is the only reliable technology for detecting and track
ing enemy diesel-electric submarines, and the President—
the Commander in Chief—has determined that training with
active sonar is “essential to national security.” Id., at 232a.
The public interest in conducting training exercises with
active sonar under realistic conditions plainly outweighs the
interests advanced by the plaintiffs. Of course, military in
terests do not always trump other considerations, and we
have not held that they do. In this case, however, the
proper determination of where the public interest lies does
not strike us as a close question.
C
1. Despite the importance of assessing the balance of equi
ties and the public interest in determining whether to grant
a preliminary injunction, the District Court addressed these
considerations in only a cursory fashion. The court’s entire
discussion of these factors consisted of one (albeit lengthy)
sentence: “The Court is also satisfied that the balance of
hardships tips in favor of granting an injunction, as the harm
to the environment, Plaintiffs, and public interest outweighs
the harm that Defendants would incur if prevented from
using MFA sonar, absent the use of effective mitigation

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measures, during a subset of their regular activities in one
part of one state for a limited period.” Id., at 217a–218a.
As the prior Ninth Circuit panel in this case put it, in staying
the District Court’s original preliminary injunction, “[t]he
district court did not give serious consideration to the public
interest factor.” 502 F. 3d, at 863. The District Court’s
order on remand did nothing to cure this defect, but simply
repeated nearly verbatim the same sentence from its previ
ous order. Compare 530 F. Supp. 2d, at 1118, with Pet. App.
217a–218a. The subsequent Ninth Circuit panel framed its
opinion as reviewing the District Court’s exercise of discre
tion, 518 F. 3d, at 697–699, but that discretion was barely
exercised here.
The Court of Appeals held that the balance of equities and
the public interest favored the plaintiffs, largely based on its
view that the preliminary injunction would not in fact im
pose a significant burden on the Navy’s ability to conduct
its training exercises and certify its strike groups. Id., at
698–699. The court deemed the Navy’s concerns about the
preliminary injunction “speculative” because the Navy had
not operated under similar procedures before. Ibid. But
this is almost always the case when a plaintiff seeks injunc
tive relief to alter a defendant’s conduct. The lower courts
failed properly to defer to senior Navy officers’ specific, pre
dictive judgments about how the preliminary injunction
would reduce the effectiveness of the Navy’s SOCAL train
ing exercises. See Wright & Miller § 2948.2, at 167–168
(“The policy against the imposition of judicial restraints
prior to an adjudication of the merits becomes more signifi
cant when there is reason to believe that the decree will
be burdensome”).
2. The preliminary injunction requires the Navy to shut
down its MFA sonar if a marine mammal is detected within
2,200 yards of a sonar-emitting vessel. The Ninth Circuit
stated that the 2,200-yard shutdown zone would not be
overly burdensome because sightings of marine mammals

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during training exercises are relatively rare. But regard
less of the frequency of marine mammal sightings, the in
junction will greatly increase the size of the shutdown zone.
Pursuant to its exemption from the MMPA, the Navy agreed
to reduce the power of its MFA sonar at 1,000 yards and 500
yards, and to completely turn off the system at 200 yards.
Pet. App. 222a–230a. The District Court’s injunction does
not include a graduated power-down, instead requiring a
total shutdown of MFA sonar if a marine mammal is detected
within 2,200 yards of a sonar-emitting vessel. There is an
exponential relationship between radius length and surface
area (Area = π r2). Increasing the radius of the shutdown
zone from 200 to 2,200 yards would accordingly expand the
surface area of the shutdown zone by a factor of over 100
(from 125,664 square yards to 15,205,308 square yards).
The lower courts did not give sufficient weight to the
views of several top Navy officers, who emphasized that be
cause training scenarios can take several days to develop,
each additional shutdown can result in the loss of several
days’ worth of training. Id., at 344a. Limiting the number
of sonar shutdowns is particularly important during the Joint
Tactical Force Exercises, which usually last for less than two
weeks. Ibid. Rear Admiral John Bird explained that the
2,200-yard shutdown zone would cause operational command
ers to “lose awareness of the tactical situation through the
constant stopping and starting of MFA [sonar].” Id., at
332a; see also id., at 356a (“It may take days to get to the
pivotal attack in antisubmarine warfare, but only minutes to
confound the results upon which certification is based”).
Even if there is a low likelihood of a marine mammal sight
ing, the preliminary injunction would clearly increase the
number of disruptive sonar shutdowns the Navy is forced to
perform during its SOCAL training exercises.
The Court of Appeals also concluded that the 2,200-yard
shutdown zone would not be overly burdensome because the
Navy had shut down MFA sonar 27 times during its eight

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prior training exercises in SOCAL; in several of these cases,
the Navy turned off its sonar when marine mammals were
spotted well beyond the Navy’s self-imposed 200-yard shut
down zone. 518 F. 3d, at 700, n. 65. Vice Admiral Samuel
Locklear III—the Commander of the Navy’s Third Fleet—
stated that any shutdowns beyond the 200-yard zone were
voluntary avoidance measures that likely took place at tacti
cally insignificant times; the Ninth Circuit discounted this
explanation as not supported by the record. Ibid. In
reaching this conclusion, the Court of Appeals ignored key
portions of Vice Admiral Locklear’s declaration, in which he
stated unequivocally that commanding officers “would not
shut down sonar until legally required to do so if in contact
with a submarine.” Pet. App. 354a–355a. Similarly, if a
commanding officer is in contact with a target submarine,
“the CO will be expected to continue to use active sonar
unless another ship or helicopter can gain contact or if regu
latory reasons dictate otherwise.” Id., at 355a. The record
supports the Navy’s contention that its shutdowns of MFA
sonar during prior training exercises only occurred during
tactically insignificant times; those voluntary shutdowns do
not justify the District Court’s imposition of a mandatory
2,200-yard shutdown zone.
Lastly, the Ninth Circuit stated that a 2,200-yard shut
down zone was feasible because the Navy had previously
adopted a 2,000-meter zone for low-frequency active (LFA)
sonar. The Court of Appeals failed to give sufficient weight
to the fact that LFA sonar is used for long-range detection
of enemy submarines, and thus its use and shutdown involve
tactical considerations quite different from those associated
with MFA sonar. See App. 508 (noting that equating MFA
sonar with LFA sonar “is completely misleading and is like
comparing 20 degrees Fahrenheit to 20 degrees Celsius”).
3. The Court of Appeals also concluded that the Navy’s
training exercises would not be significantly affected by the
requirement that it power down MFA sonar by 6 dB during

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significant surface ducting conditions. Again, we think the
Ninth Circuit understated the burden this requirement
would impose on the Navy’s ability to conduct realistic train
ing exercises.
Surface ducting is a phenomenon in which relatively little
sound energy penetrates beyond a narrow layer near the
surface of the water. When surface ducting occurs, active
sonar becomes more useful near the surface but less useful
at greater depths. Pet. App. 299a–300a. Diesel-electric
submariners are trained to take advantage of these distor
tions to avoid being detected by sonar. Id., at 333a.
The Ninth Circuit determined that the power-down re
quirement during surface ducting conditions was unlikely to
affect certification of the Navy’s strike groups because sur
face ducting occurs relatively rarely, and the Navy has pre
viously certified strike groups that did not train under such
conditions. 518 F. 3d, at 701–702. This reasoning is back
wards. Given that surface ducting is both rare and unpre
dictable, it is especially important for the Navy to be able to
train under these conditions when they occur. Rear Admi
ral Bird explained that the 6 dB power-down requirement
makes the training less valuable because it “exposes [sonar
operators] to unrealistically lower levels of mutual interfer
ence caused by multiple sonar systems operating together by
the ships within the Strike Group.” Pet. App. 281a (foot
note and some capitalization omitted). Although a 6 dB re
duction may not seem terribly significant, decibels are meas
ured on a logarithmic scale, so a 6 dB decrease in power
equates to a 75% reduction. Id., at 284a–285a.
4. The District Court acknowledged that “ ‘the imposition
of these mitigation measures will require the Navy to alter
and adapt the way it conducts antisubmarine warfare train
ing—a substantial challenge. Nevertheless, evidence pre
sented to the Court reflects that the Navy has employed mit
igation measures in the past, without sacrificing training

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objectives.’ ” 527 F. Supp. 2d, at 1238. Apparently no good
deed goes unpunished. The fact that the Navy has taken
measures in the past to address concerns about marine mam
mals—or, for that matter, has elected not to challenge four
additional restrictions imposed by the District Court in this
case, see supra, at 17–19—hardly means that other, more in
trusive restrictions pose no threat to preparedness for war.
The Court of Appeals concluded its opinion by stating that
“the Navy may return to the district court to request relief
on an emergency basis” if the preliminary injunction “actu
ally result[s] in an inability to train and certify sufficient
naval forces to provide for the national defense.” 518 F. 3d,
at 703. This is cold comfort to the Navy. The Navy con
tends that the injunction will hinder efforts to train sonar
operators under realistic conditions, ultimately leaving
strike groups more vulnerable to enemy submarines. Un
like the Ninth Circuit, we do not think the Navy is required
to wait until the injunction “actually result[s] in an inability
to train . . . sufficient naval forces to provide for the national
defense” before seeking its dissolution. By then it may be
too late.
IV
As noted above, we do not address the underlying merits
of plaintiffs’ claims. While we have authority to proceed to
such a decision at this point, see Munaf, 553 U. S., at 691–
692, doing so is not necessary here. In addition, reaching
the merits is complicated by the fact that the lower courts
addressed only one of several issues raised, and plaintiffs
have largely chosen not to defend the decision below on
that ground.5
5 The bulk of Justice Ginsburg’s dissent is devoted to the merits. For
the reasons stated, we find the injunctive relief granted in this case
an abuse of discretion, even if plaintiffs are correct on the underlying
merits. As to the injunction, the dissent barely mentions the Navy’s in

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At the same time, what we have said makes clear that it
would be an abuse of discretion to enter a permanent injunc
tion, after final decision on the merits, along the same lines
as the preliminary injunction. An injunction is a matter of
equitable discretion; it does not follow from success on the
merits as a matter of course. Romero-Barcelo, 456 U. S., at
313 (“[A] federal judge sitting as chancellor is not mechani
cally obligated to grant an injunction for every violation of
law”).
The factors examined above—the balance of equities and
consideration of the public interest—are pertinent in assess
ing the propriety of any injunctive relief, preliminary or per
manent. See Amoco Production Co., 480 U. S., at 546, n. 12
(“The standard for a preliminary injunction is essentially the
same as for a permanent injunction with the exception that
the plaintiff must show a likelihood of success on the merits
rather than actual success”). Given that the ultimate legal
claim is that the Navy must prepare an EIS, not that it must
cease sonar training, there is no basis for enjoining such
terests. Post, at 53. We find that those interests, and the documented
risks to national security, clearly outweigh the harm on the other side of
the balance.
We agree with much of Justice Breyer’s analysis, post, at 36–41 (opin
ion concurring in part and dissenting in part), but disagree with his conclu
sion that the modified conditions imposed by the stay order should remain
in force until the Navy completes its EIS, post, at 42–43. The Court is
reviewing the District Court’s imposition of the preliminary injunction;
once we conclude, as Justice Breyer does, post, at 41, that the prelimi
nary injunction should be vacated, the stay order is no longer pertinent.
A stay is a useful tool for managing the impact of injunctive relief pending
further appeal, but once the Court resolves the merits of the appeal, the
stay ceases to be relevant. See 518 F. 3d 704, 706 (CA9 2008) (“[T]he
partial stay . . . shall remain in effect until final disposition by the Supreme
Court”). Unexamined conditions imposed by the stay order are certainly
no basis for what would be in effect the entry of a new preliminary injunc
tion by this Court.

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training in a manner credibly alleged to pose a serious threat
to national security. This is particularly true in light of the
fact that the training has been going on for 40 years with no
documented episode of harm to a marine mammal. A court
concluding that the Navy is required to prepare an EIS has
many remedial tools at its disposal, including declaratory re
lief or an injunction tailored to the preparation of an EIS
rather than the Navy’s training in the interim. See, e. g.,
Steffel v. Thompson, 415 U. S. 452, 466 (1974) (“Congress
plainly intended declaratory relief to act as an alternative to
the strong medicine of the injunction”). In the meantime,
we see no basis for jeopardizing national security, as the
present injunction does. Plaintiffs confirmed at oral argu
ment that the preliminary injunction was “the whole ball
game,” Tr. of Oral Arg. 33, and our analysis of the propriety
of preliminary relief is applicable to any permanent injunc
tion as well.
* * *
President Theodore Roosevelt explained that “the only
way in which a navy can ever be made efficient is by practice
at sea, under all the conditions which would have to be met
if war existed.” President’s Annual Message, 42 Cong. Rec.
81 (1907). We do not discount the importance of plaintiffs’
ecological, scientific, and recreational interests in marine
mammals. Those interests, however, are plainly out
weighed by the Navy’s need to conduct realistic training ex
ercises to ensure that it is able to neutralize the threat posed
by enemy submarines. The District Court abused its dis
cretion by imposing a 2,200-yard shutdown zone and by re
quiring the Navy to power down its MFA sonar during sig
nificant surface ducting conditions. The judgment of the
Court of Appeals is reversed, and the preliminary injunction
is vacated to the extent it has been challenged by the Navy.
It is so ordered.

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Justice Breyer, with whom Justice Stevens joins as
to Part I, concurring in part and dissenting in part.
As of December 2006, the United States Navy planned
to engage in a series of 14 antisubmarine warfare training
exercises off the southern California coast. The Natural
Resources Defense Council, Inc., and others (NRDC)
brought this case in Federal District Court claiming that the
National Environmental Policy Act of 1969 (NEPA) requires
the Navy to prepare an environmental impact statement
(EIS) (assessing the impact of the exercises on marine mam
mals) prior to its engaging in the exercises. As the case
reaches us, the District Court has found that the NRDC will
likely prevail on its demand for an EIS; the Navy has agreed
to prepare an EIS; the District Court has forbidden the
Navy to proceed with the exercises unless it adopts six miti
gating measures; and the Navy has agreed to adopt all but
two of those measures.
The controversy between the parties now concerns the
two measures that the Navy is unwilling to adopt. The first
concerns the “shutdown zone,” a circle with a ship at the
center within which the Navy must try to spot marine mam
mals and shut down its sonar if one is found. The contro
verted condition would enlarge the radius of that circle from
about one-tenth of a mile (200 yards) to one and one-quarter
miles (2,200 yards). The second concerns special ocean con
ditions called “surface ducting conditions.” The contro
verted condition would require the Navy, when it encounters
any such condition, to diminish the sonar’s power by 75%.
The Court of Appeals affirmed the District Court order that
contained these two conditions. 518 F. 3d 658, 703 (CA9
2008).
I
We must now decide whether the District Court was le
gally correct in forbidding the training exercises unless the
Navy implemented the two controverted conditions. In

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doing so, I assume, like the Court, that the NRDC will pre
vail on its demand for an EIS. (Indeed, the Navy is in the
process of preparing one.) And, I would ask whether, in
imposing these conditions, the District Court properly “bal
ance[d the] harms.” See, e. g., Amoco Production Co. v.
Gambell, 480 U. S. 531, 545 (1987).
Respondents’ (the plaintiffs) argument favoring the Dis
trict Court injunction is a strong one. As Justice Gins
burg well points out, see post, at 47–48 (dissenting opinion),
the very point of NEPA’s insistence upon the writing of an
EIS is to force an agency “carefully” to “consider . . . detailed
information concerning significant environmental impacts,”
while “giv[ing] the public the assurance that the agency ‘has
indeed considered environmental concerns in its decision
making process.’ ” Robertson v. Methow Valley Citizens
Council, 490 U. S. 332, 349 (1989). NEPA seeks to assure
that when Government officials consider taking action that
may affect the environment, they do so fully aware of the
relevant environmental considerations. An EIS does not
force them to make any particular decision, but it does lead
them to take environmental considerations into account
when they decide whether, or how, to act. Id., at 354.
Thus, when a decision to which EIS obligations attach is
made without the informed environmental consideration that
NEPA requires, much of the harm that NEPA seeks to pre
vent has already taken place. In this case, for example, the
absence of an injunction means that the Navy will proceed
with its exercises in the absence of the fuller consideration
of environmental effects that an EIS is intended to bring.
The absence of an injunction thereby threatens to cause the
very environmental harm that a full preaction EIS might
have led the Navy to avoid (say, by adopting the two addi
tional mitigation measures that the NRDC proposes). Con
sequently, if the exercises are to continue, conditions de
signed to mitigate interim environmental harm may well be
appropriate.

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On the other hand, several features of this case lead me to
conclude that the record, as now before us, lacks adequate
support for an injunction imposing the two controverted re
quirements. First, the evidence of need for the two special
conditions is weak or uncertain. The record does show that
the exercises as the Navy originally proposed them could
harm marine mammals. The District Court found (based on
the Navy’s study of the matter) that the exercises might
cause 466 instances of Level A harm and 170,000 instances
of Level B harm. App. to Pet. for Cert. 196a–197a. (The
environmental assessment actually predicted 564 instances
of Level A harm. See App. 223–224.) The study defines
Level A injury as “any act that injures or has the significant
potential to injure a marine mammal or marine mammal
stock in the wild” through “destruction or loss of biological
tissue,” whether “slight to severe.” Id., at 160. It defines
Level B harm as “ ‘any act that disturbs or is likely to disturb
a marine mammal . . . by causing disruption of natural behav
ioral patterns including, but not limited to, migration, surfac
ing, nursing, breeding, feeding, or sheltering to a point where
such behaviors are abandoned or significantly altered’ ” and
describes it as a “short term” and “temporary” “disturb
ance.” Id., at 161, 175.
The raw numbers seem large. But the parties argue
about the extent to which they mean likely harm. The
Navy says the classifications and estimates err on the side
of caution. (When in doubt about the amount of harm to a
mammal, the study assumed the harm would qualify as Level
A harassment. Id., at 200.) The Navy also points out that,
by definition, mammals recover from Level B injuries, often
very quickly. It notes that, despite 40 years of naval exer
cises off the southern California coast, no injured marine
mammal has ever been found. App. to Pet. for Cert. 274a–
275a. (It adds that dolphins often swim alongside the ships.
Id., at 290a, 346a.) At the same time, plaintiffs point to in
stances where whales have been found stranded. They add

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that scientific studies have found a connection between those
beachings and the Navy’s use of sonar, see, e. g., App. 600–
602, and the Navy has acknowledged one stranding where
“U. S. Navy mid-frequency sonar has been identified as the
most plausible contributory source to the stranding event,”
id., at 168.
Given the uncertainty the figures create in respect to the
harm caused by the Navy’s original training plans, it would
seem important to have before us at least some estimate of
the harm likely avoided by the Navy’s decision not to contest
here four of the six mitigating conditions that the District
Court ordered. Without such evidence, it is difficult to as
sess the relevant harm—that is, the environmental harm
likely caused by the Navy’s exercises with the four uncon
tested mitigation measures (but without the two contested
mitigation measures) in place.
Second, the Navy has filed multiple affidavits from Navy
officials explaining in detail the seriousness of the harm that
the delay associated with completion of this EIS (approxi
mately one year) would create in respect to the Navy’s abil
ity to maintain an adequate national defense. See generally
App. to Pet. for Cert. 260a–357a. Taken by themselves,
those affidavits make a strong case for the proposition that
insistence upon the two additional mitigating conditions
would seriously interfere with necessary defense training.
The affidavits explain the importance of training in anti
submarine warfare, id., at 263a; the need to use active sonar
to detect enemy submarines, id., at 266a–267a, App. 566; the
complexity of a training exercise involving sonar, App. to
Pet. for Cert. 343a; the need for realistic conditions when
training exercises take place, id., at 299a–300a, App. 566; the
“cascading” negative “effect” that delay in one important as
pect of a set of coordinated training exercises has upon the
Navy’s ability “to provide combat ready forces,” App. to Pet.
for Cert. 343a; the cost and disruption that would accompany
the adoption of the two additional mitigating conditions that

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the NRDC seeks, ibid.; the Navy’s resulting inability ade
quately to train personnel, id., at 278a; the effectiveness of
the mammal-protecting measures that the Navy has taken
in the past, id., at 285a–298a; and the reasonable likelihood
that the mitigating conditions to which it has agreed will
prove adequate, id., at 296a.
Third, and particularly important in my view, the District
Court did not explain why it rejected the Navy’s affidavit
supported contentions. In its first opinion enjoining the use
of sonar, the District Court simply stated:
“The Court is . . . satisfied that the balance of hardships
tips in favor of granting an injunction, as the harm to
the environment, Plaintiffs, and public interest out
weighs the harm that Defendants would incur if pre
vented from using [mid-frequency active (MFA)] sonar,
absent the use of effective mitigation measures, during
a subset of their regular activities in one part of one
state for a limited period.” Id., at 217a–218a.
Following remand from the Court of Appeals, the District
Court simply repeated, word for word, this same statement.
It said:
“The Court is . . . satisfied that the balance of hardships
tips in favor of granting an injunction, as the harm to
the environment, Plaintiffs, and public interest out
weighs the harm that Defendants would incur (or the
public interest would suffer) if Defendants were pre
vented from using MFA sonar, absent the use of effec
tive mitigation measures, during a subset of their regu
lar activities in one part of one state for a limited
period.” 530 F. Supp. 2d 1110, 1118 (CD Cal. 2008).
With respect to the imposition of the 2,200-yard shutdown
zone, the District Court noted evidence of the harm that
MFA sonar poses to marine mammals, and then concluded
that “[t]he Court therefore is persuaded that while the 2200
yard shutdown requirement may protect marine mammals

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from the harshest of sonar-related consequences, it repre
sents a minimal imposition [on] the Navy’s training exer
cises.” Id., at 1119. The District Court did not there ex
plain the basis for that conclusion. With respect to the
imposition of the surface ducting condition, the District
Court said nothing about the Navy’s interests at all. Id.,
at 1120–1121.
While a district court is often free simply to state its con
clusion in summary fashion, in this instance neither that con
clusion, nor anything else I have found in the District Court’s
opinion, answers the Navy’s documented claims that the two
extra conditions the District Court imposed will, in effect,
seriously interfere with its ability to carry out necessary
training exercises.
The first condition requires the Navy to reduce the power
of its sonar equipment by 75% when the ship encounters a
condition called “surface ducting” that occurs when the pres
ence of layers of water of different temperature make it un
usually difficult for sonar operators to determine whether a
diesel submarine is hiding below. Rear Admiral John Bird,
an expert in submarine warfare, made clear that the 75%
power-reduction requirement was equivalent to forbidding
any related training. App. to Pet. for Cert. 297a. But he
says in paragraph 52 of his declaration: “Training in surface
ducting conditions is critical to effective training because
sonar operators need to learn how sonar transmissions are
altered due to surface ducting and how submarines may take
advantage of them. ” Id., at 299a– 300a. The District
Court, as far as I can tell, did not even acknowledge in its
opinion the Navy’s asserted interest in being able to train
under these conditions. 530 F. Supp. 2d, at 1120–1121.
The second condition requires the Navy to expand the
sonar “shutdown” area surrounding a ship (i. e., turn off the
sonar if a mammal is spotted in the area) from a circle with
a radius of about one-tenth of a mile to a circle with a radius
of about one mile and a quarter. Both sides agree that this

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requirement will lead to more shutdowns. Admiral Gary
Roughead, Chief of Naval Operations, states in paragraph 12
of his declaration that this expanded zone requirement “will
result in increased interruptions to training exercises, . . .
vastly increas[ing] the risk of negating training effective
ness, preventing strike group certification, and disrupting
carefully orchestrated deployment plans to meet world-wide
operational commitments.” App. to Pet. for Cert. 344a.
Again, I can find nothing in the District Court’s opinion that
specifically explains why this is not so. 530 F. Supp. 2d, at
1119–1120.
Fourth, the Court of Appeals sought, through its own thor
ough examination of the record, to supply the missing expla
nations. But those explanations are not sufficient. In re
spect to the surface ducting conditions, the Court of Appeals
rejected the Navy’s contentions on the ground that those
conditions are “rar[e],” and the Navy has certified trainings
that did not involve any encounter with those conditions.
518 F. 3d, at 701–702. I am not certain, however, why the
rarity of the condition supports the District Court’s conclu
sion. Rarity argues as strongly for training when the condi
tion is encountered as it argues for the contrary.
In respect to the expansion of the “shutdown” area, the
Court of Appeals noted that (1) the Navy in earlier exercises
had shut down its sonar when marine mammals were sited
within about one-half a mile, (2) the Navy has used a larger
shutdown area when engaged in exercises with lower fre
quency sonar equipment, and (3) foreign navies have used
larger shutdown areas. Id., at 699–701, and nn. 63, 67. But
the Navy’s affidavits state that (1) earlier shutdowns when
marine mammals were spotted at farther distances “likely
occurred during tactically insignificant times,” App. to Pet.
for Cert. 356a, (2) ships with low frequency sonar (unlike the
sonar here at issue) have equipment that makes it easier to
monitor the larger area, particularly by significantly reduc
ing the number of monitoring personnel necessarily involved,
and (3) foreign navy experience is not relevant given the

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potentially different military demands upon those navies,
App. 508–509.
Finally, the Court of Appeals, mirroring a similar District
Court suggestion in the language I have quoted, says that
“the exercises in southern California are only a subset of the
Navy’s training activities involving active sonar.” 518 F. 3d,
at 702. It adds that the Navy’s study “shows the Navy is
still able to conduct its exercises in alternative locations, in
reduced number, or through simulation.” Ibid., n. 69. The
Court of Appeals, however, also concluded that the study
“provides reasonably detailed justifications for why the
Southern California Operating Area is uniquely suited to
these exercises, and demonstrates that the Navy would suf
fer a certain hardship if the considered alternatives were
employed instead.” Ibid.
Fifth, when the Court of Appeals first heard this case fol
lowing the District Court’s imposition of a broad, absolute
injunction, it held that any injunction must be crafted so that
the Navy could continue its training exercises. Noting that
the Navy had, in the past, been able to use mitigation meas
ures to “reduce the harmful effects of its active sonar,” it
“vacate[d] the stay and remand[ed] this matter to the district
court to narrow its injunction so as to provide mitigation
conditions under which the Navy may conduct its training
exercises.” 508 F. 3d 885, 887 (CA9 2007) (emphasis added).
For the reasons just stated, neither the District Court nor
the Court of Appeals has explained why we should reject
the Navy’s assertions that it cannot effectively conduct its
training exercises under the mitigation conditions imposed
by the District Court.
I would thus vacate the preliminary injunction imposed by
the District Court to the extent it has been challenged by
the Navy. Neither the District Court nor the Court of Ap
peals has adequately explained its conclusion that the bal
ance of the equities tips in favor of plaintiffs. Nor do those
parts of the record to which the parties have pointed supply
the missing explanation.

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II
Nonetheless, as the Court of Appeals held when it first
considered this case, the Navy’s past use of mitigation condi
tions makes clear that the Navy can effectively train under
some mitigation conditions. In the ordinary course, I would
remand so the District Court could, pursuant to the Court
of Appeals’ direction, set forth mitigation conditions that will
protect the marine wildlife while also enabling the Navy to
carry out its exercises. But, at this point, the Navy has in
formed us that this set of exercises will be complete by Janu
ary, at the latest, and an EIS will likely be complete at that
point, as well. Thus, by the time the District Court would
have an opportunity to impose new conditions, the case could
very well be moot.
In February of this year, the Court of Appeals stayed the
injunction imposed by the District Court—but only pending
this Court’s resolution of the case. The Court of Appeals
concluded that “[i]n light of the short time before the Navy is
to commence its next exercise, the importance of the Navy’s
mission to provide for the national defense and the represen
tation by the Chief of Naval Operations that the district
court’s preliminary injunction in its current form will ‘unac
ceptably risk’ effective training and strike group certification
and thereby interfere with his statutory responsibility . . . to
‘organiz[e], train[ ], and equip[ ] the Navy,’ ” interim relief
was appropriate, and the court then modified the two mitiga
tion conditions at issue. 518 F. 3d 704, 705 (CA9 2008).
With respect to the 2,200-yard shutdown zone, it required
the Navy to suspend its use of the sonar if a marine mammal
is detected within 2,200 yards, except when sonar is being
used at a “critical point in the exercise,” in which case the
amount by which the Navy must power down is proportional
to the mammal’s proximity to the sonar. Id., at 705–706 (in
ternal quotation marks omitted). With respect to surface
ducting, the Navy is only required to shut down sonar alto

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gether when a marine mammal is detected within 500 meters
and the amount by which it is otherwise required to power
down is again proportional to the mammal’s proximity to the
sonar source. Ibid. The court believed these conditions
would permit the Navy to go forward with its imminently
planned exercises while at the same time minimizing the
harm to marine wildlife.
In my view, the modified conditions imposed by the Court
of Appeals in its February stay order reflect the best equita
ble conditions that can be created in the short time available
before the exercises are complete and the EIS is ready. The
Navy has been training under these conditions since Febru
ary, so allowing them to remain in place will, in effect, main
tain what has become the status quo. Therefore, I would
modify the Court of Appeals’ February 29, 2008, order so
that the provisional conditions it contains remain in place
until the Navy’s completion of an acceptable EIS.
Justice Ginsburg, with whom Justice Souter joins,
dissenting.
The central question in this action under the National En
vironmental Policy Act of 1969 (NEPA) was whether the
Navy must prepare an environmental impact statement
(EIS). The Navy does not challenge its obligation to do so,
and it represents that the EIS will be complete in January
2009—one month after the instant exercises conclude. If
the Navy had completed the EIS before taking action, as
NEPA instructs, the parties and the public could have bene
fited from the environmental analysis—and the Navy’s train
ing could have proceeded without interruption. Instead,
the Navy acted first, and thus thwarted the very purpose an
EIS is intended to serve. To justify its course, the Navy
sought dispensation not from Congress, but from an execu
tive council that lacks authority to countermand or revise
NEPA’s requirements. I would hold that, in imposing man
ageable measures to mitigate harm until completion of the

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EIS, the District Court conscientiously balanced the equities
and did not abuse its discretion.
I
In December 2006, the Navy announced its intent to pre
pare an EIS to address the potential environmental effects
of its naval readiness activities in the Southern California
(SOCAL) Range Complex. See 71 Fed. Reg. 76639 (2006).
These readiness activities include expansion and intensifica
tion of naval training, as well as research, development, and
testing of various systems and weapons. Id., at 76639,
76640. The EIS process is underway, and the Navy repre
sents that it will be complete in January 2009. Brief for
Petitioners 11; Tr. of Oral Arg. 11.
In February 2007, seeking to commence training before
completion of the EIS, the Navy prepared an environmental
assessment (EA) for the 14 exercises it planned to undertake
in the interim. See App. to Pet. for Cert. 235a.1 On Febru
ary 12, the Navy concluded the EA with a finding of no sig
nificant impact. App. 225–226. The same day, the Navy
commenced its training exercises. Id., at 227 (“The Pro
posed Action is hereby implemented.”).
On March 22, 2007, the Natural Resources Defense Coun
cil, Inc. (NRDC), filed suit in the U. S. District Court for
the Central District of California, seeking declaratory and
injunctive relief based on the Navy’s alleged violations of
NEPA and other environmental statutes. As relevant here,
the District Court determined that NRDC was likely to suc
ceed on its NEPA claim and that equitable principles war
ranted preliminary relief. On August 7, 2007, the court
1 An EA is used “for determining whether to prepare” an EIS. Depart
ment of Transportation v. Public Citizen, 541 U. S. 752, 757 (2004) (quot
ing 40 CFR § 1508.9(a) (2003)); see ante, at 15–16 (opinion of the Court).
By definition, an EA alone does not satisfy an agency’s obligation under
NEPA if the effects of a proposed action require preparation of a full EIS.

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enjoined the Navy’s use of mid-frequency active (MFA) sonar
during the 11 remaining exercises at issue.
On August 31, the Court of Appeals for the Ninth Circuit
stayed the injunction pending disposition of the Navy’s ap
peal, and the Navy proceeded with two more exercises. In
a November 13 order, the Court of Appeals vacated the stay,
stating that NRDC had shown “a strong likelihood of success
on the merits” and that preliminary injunctive relief was ap
propriate. 508 F. 3d 885, 886 (2007). The Court of Appeals
remanded, however, instructing the District Court to pro
vide mitigation measures under which the Navy could con
duct its remaining exercises.
On remand, the District Court received briefing from both
parties. In addition, the court “toured the USS Milius at
the naval base in San Diego, California, to improve its under
standing of the Navy’s sonar training procedures and the fea
sibility of the parties’ proposed mitigation measures. Coun
sel for both [parties] were present.” 530 F. Supp. 2d 1110,
1112 (2008). On January 3, 2008, the District Court entered
a modified preliminary injunction imposing six mitigation
measures. The court revised the modified injunction
slightly on January 10 in response to filings by the Navy,
and four days later, denied the Navy’s application for a stay
pending appeal.
On the following day, January 15, the Council on Environ
mental Quality (CEQ), an advisory body within the Execu
tive Office of the President, responded to the Navy’s request
for “alternative arrangements” for NEPA compliance. App.
to Pet. for Cert. 233a. The “arrangements” CEQ set
out purported to permit the Navy to continue its training
without timely environmental review. Id., at 241a–247a.
The Navy accepted the arrangements on the same day.
App. 228.
The Navy then filed an emergency motion in the Court
of Appeals requesting immediate vacatur of the District
Court’s modified injunction. CEQ’s action, the Navy urged,

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eliminated the injunction’s legal foundation. In the alterna
tive, the Navy sought a stay of two aspects of the injunction
pending its appeal: the 2,200-yard mandatory shutdown zone
and the power-down requirement in significant surface duct
ing conditions, see ante, at 17–18 (opinion of the Court).
While targeting in its stay application only two of the six
measures imposed by the District Court, the Navy explicitly
reserved the right to challenge on appeal each of the six
mitigation measures. Responding to the Navy’s emergency
motion, the Court of Appeals remanded the matter to allow
the District Court to determine in the first instance the ef
fect of the intervening executive action. Pending its own
consideration of the Navy’s motion, the District Court stayed
the injunction, and the Navy conducted its sixth exercise.
On February 4, after briefing and oral argument, the Dis
trict Court denied the Navy’s motion. The Navy appealed,
reiterating its position that CEQ’s action eliminated all justi
fication for the injunction. The Navy also argued that vaca
tur of the entire injunction was required irrespective of
CEQ’s action, in part because the “conditions imposed, in
particular the 2,200 yard mandatory shutdown zone and the
six decibel (75%) power-down in significant surface ducting
conditions, severely degrade the Navy’s training.” Brief for
Appellants in No. 08–55054 (CA9), p. 15. In the February
29 decision now under review, the Court of Appeals affirmed
the District Court’s judgment. 518 F. 3d 658, 703 (2008).
The Navy has continued training in the meantime and plans
to complete its final exercise in December 2008.
As the procedural history indicates, the courts below de
termined that an EIS was required for the 14 exercises.
The Navy does not challenge that decision in this Court.
Instead, the Navy defends its failure to complete an EIS
before launching the exercises based upon CEQ’s “alterna
tive arrangements”—arrangements the Navy sought and ob
tained in order to overcome the lower courts’ rulings. As

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explained below, the Navy’s actions undermined NEPA and
took an extraordinary course.
II
NEPA “promotes its sweeping commitment” to environ
mental integrity “by focusing Government and public atten
tion on the environmental effects of proposed agency action.”
Marsh v. Oregon Natural Resources Council, 490 U. S. 360,
371 (1989). “By so focusing agency attention, NEPA en
sures that the agency will not act on incomplete information,
only to regret its decision after it is too late to correct.”
Ibid.
The EIS is NEPA’s core requirement. Department of
Transportation v. Public Citizen, 541 U. S. 752, 757 (2004).
This Court has characterized the requirement as “action
forcing.” Andrus v. Sierra Club, 442 U. S. 347, 350 (1979)
(internal quotation marks omitted). Environmental con
cerns must be “integrated into the very process of agency
decisionmaking” and “interwoven into the fabric of agency
planning.” Id., at 350–351. In addition to discussing poten
tial consequences, an EIS must describe potential mitigation
measures and alternatives to the proposed course of action.
See Robertson v. Methow Valley Citizens Council, 490 U. S.
332, 351–352 (1989) (citing 40 CFR §§ 1508.25(b), 1502.14(f),
1502.16(h), 1505.2(c) (1987)). The EIS requirement “ensures
that important effects will not be overlooked or under
estimated only to be discovered after resources have been
committed or the die otherwise cast.” 490 U. S., at 349.
“Publication of an EIS . . . also serves a larger informa
tional role.” Ibid. It demonstrates that an agency has in
deed considered environmental concerns, and “perhaps more
significantly, provides a springboard for public comment.”
Ibid. At the same time, it affords other affected govern
mental bodies “notice of the expected consequences and the
opportunity to plan and implement corrective measures in a
timely manner.” Id., at 350.

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In light of these objectives, the timing of an EIS is critical.
CEQ regulations instruct agencies to “integrate the NEPA
process with other planning at the earliest possible time to
insure that planning and decisions reflect environmental val
ues.” 40 CFR § 1501.2 (1987). An EIS must be prepared
“early enough so that it can serve practically as an important
contribution to the decisionmaking process and will not be
used to rationalize or justify decisions already made.” An
drus, 442 U. S., at 351–352, n. 3 (quoting 43 Fed. Reg. 55995
(1978) (codified in 40 CFR § 1502.5 (1979))).
The Navy’s publication of its EIS in this case, scheduled to
occur after the 14 exercises are completed, defeats NEPA’s
informational and participatory purposes. The Navy’s in
verted timing, it bears emphasis, is the very reason why the
District Court had to confront the question of mitigation
measures at all. Had the Navy prepared a legally sufficient
EIS before beginning the SOCAL exercises, NEPA would
have functioned as its drafters intended: The EIS process
and associated public input might have convinced the Navy
voluntarily to adopt mitigation measures, but NEPA itself
would not have impeded the Navy’s exercises. See Pub
lic Citizen, 541 U. S., at 756, 769, n. 2 (noting that NEPA
does not mandate particular results, but rather establishes
procedural requirements with a “focus on improving agency
decisionmaking”).
The Navy had other options. Most importantly, it could
have requested assistance from Congress. The Government
has sometimes obtained congressional authorization to pro
ceed with planned activities without fulfilling NEPA’s re
quirements. See, e. g., Floyd D. Spence National Defense
Authorization Act for Fiscal Year 2001, Pub. L. 106–398,
§ 317, 114 Stat. 1654A–57 (exempting the military from pre
paring a programmatic EIS for low-level flight training); 42
U. S. C. § 10141(c) (2000 ed.) (exempting the Environmental
Protection Agency from preparing an EIS for the develop
ment of criteria for handling spent nuclear fuel and high

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49 Cite as: 555 U. S. 7 (2008)
Ginsburg, J., dissenting
level radioactive waste); 43 U. S. C. § 1652(d) (exempting con
struction of the trans-Alaska oil pipeline from further
NEPA compliance).
Rather than resorting to Congress, the Navy “sought re
lief from the Executive Branch.” Ante, at 18 (opinion of the
Court). On January 10, 2008, the Navy asked CEQ, adviser
to the President, to approve alternative arrangements for
NEPA compliance pursuant to 40 CFR § 1506.11 (1987).
App. to Pet. for Cert. 233a; see ante, at 18, n. 3. The next
day, the Navy submitted supplementary material to CEQ,
including the Navy’s EA and after-action reports, the Dis
trict Court’s orders, and two analyses by the National Ma
rine Fisheries Service (NMFS). App. to Pet. for Cert.
237a–238a. Neither the Navy nor CEQ notified NRDC, and
CEQ did not request or consider any of the materials under
lying the District Court orders it addressed.
Four days later, on January 15, the Chairman of CEQ is
sued a letter to the Secretary of the Navy. Repeating the
Navy’s submissions with little independent analysis, the let
ter stated that the District Court’s orders posed risks to the
Navy’s training exercises. See id., at 238a (“You have ex
plained that the training restrictions set forth in the . . .
injunctive orders prevent the Navy from providing Strike
Groups with adequate proficiency training and create a sub
stantial risk of precluding certification of the Strike Groups
as combat ready.”).
The letter continued:
“Discussions between our staffs, your letter and sup
porting documents, and the classified declaration and
briefings I have received, have clearly determined that
the Navy cannot ensure the necessary training to certify
strike groups for deployment under the terms of the in
junctive orders. Based on the record supporting your
request . . . CEQ has concluded that the Navy must be
able to conduct the [exercises] . . . in a timeframe that
does not provide sufficient time to complete an EIS.

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50 WINTER v. NATURAL RESOURCES DEFENSE
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Therefore, emergency circumstances are present for the
nine exercises and alternative arrangements for compli
ance with NEPA under CEQ regulation 40 C. F. R.
§ 1506.11 are warranted.” Id., at 240a.
The alternative arrangements CEQ set forth do not vindi
cate NEPA’s objectives. The arrangements provide for
“public participation measures,” which require the Navy to
provide notices of the alternative arrangements. Id., at
241a, 242a. The notices must “seek input on the process for
reviewing post-exercise assessments” and “include an offer
to meet jointly with Navy representatives . . . and CEQ to
discuss the alternative arrangements.” Id., at 242a–243a.
The alternative arrangements also describe the Navy’s exist
ing research and mitigation efforts. Id., at 243a–247a.
CEQ’s hasty decision on a one-sided record is no substitute
for the District Court’s considered judgment based on a
two-sided record.2 More fundamentally, even an exemplary
CEQ review could not have effected the short circuit the
Navy sought. CEQ lacks authority to absolve an agency of
its statutory duty to prepare an EIS. NEPA established
CEQ to assist and advise the President on environmental
policy, 42 U. S. C. § 4342, and a 1977 Executive Order charged
CEQ with issuing regulations to federal agencies for imple
mentation of NEPA’s procedural provisions, Exec. Order
No. 11991, 3 CFR 123 (1977 Comp.). This Court has recog
nized that CEQ’s regulations are entitled to “substantial def
erence,” Robertson, 490 U. S., at 355, and 40 CFR § 1506.11
indicates that CEQ may play an important consultative role
in emergency circumstances, but we have never suggested
that CEQ could eliminate the statute’s command. If the
2 The District Court may well have given too spare an explanation for
the balance of hardships in issuing its injunction of August 7, 2007. The
court cured any error in this regard, however, when it closely examined
each mitigation measure in issuing the modified injunction of January 3,
2008. The Court of Appeals, too, conducted a detailed analysis of the
record.

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51 Cite as: 555 U. S. 7 (2008)
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Navy sought to avoid its NEPA obligations, its remedy lay
in the Legislative Branch. The Navy’s alternative course—
rapid, self-serving resort to an office in the White House—is
surely not what Congress had in mind when it instructed
agencies to comply with NEPA “to the fullest extent possi
ble.” 42 U. S. C. § 4332.3
III
A
Flexibility is a hallmark of equity jurisdiction. “The es
sence of equity jurisdiction has been the power of the Chan
cellor to do equity and to mould each decree to the necessi
ties of the particular case. Flexibility rather than rigidity
has distinguished it.” Weinberger v. Romero-Barcelo, 456
U. S. 305, 312 (1982) (quoting Hecht Co. v. Bowles, 321 U. S.
321, 329 (1944)). Consistent with equity’s character, courts
do not insist that litigants uniformly show a particular, pre
determined quantum of probable success or injury before
awarding equitable relief. Instead, courts have evaluated
claims for equitable relief on a “sliding scale,” sometimes
awarding relief based on a lower likelihood of harm when
the likelihood of success is very high. 11A C. Wright,
A. Miller, & M. Kane, Federal Practice and Procedure
§ 2948.3, p. 195 (2d ed. 1995). This Court has never rejected
that formulation, and I do not believe it does so today.
Equity’s flexibility is important in the NEPA context.
Because an EIS is the tool for uncovering environmental
harm, environmental plaintiffs may often rely more heavily
on their probability of success than the likelihood of harm.
The Court is correct that relief is not warranted “simply to
prevent the possibility of some remote future injury.” Ante,
3 On the same day that CEQ issued its letter, the President granted the
Navy an exemption from the requirements of the Coastal Zone Manage
ment Act of 1972 (CZMA) pursuant to 16 U. S. C. § 1456(c)(1)(B) (2006 ed.).
That exemption, expressly authorized by the CZMA, does not affect
NRDC’s NEPA claim.

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52 WINTER v. NATURAL RESOURCES DEFENSE
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at 22 (quoting Wright & Miller, supra, § 2948.1, at 155).
“However, the injury need not have been inflicted when ap
plication is made or be certain to occur; a strong threat
of irreparable injury before trial is an adequate basis.”
Wright & Miller, supra, § 2948.1, at 155–156 (footnote omit
ted). I agree with the District Court that NRDC made the
required showing here.
B
The Navy’s own EA predicted substantial and irreparable
harm to marine mammals. Sonar is linked to mass strand
ings of marine mammals, hemorrhaging around the brain and
ears, acute spongiotic changes in the central nervous system,
and lesions in vital organs. E. g., App. 600–602; id., at 360–
362, 478–479. As the Ninth Circuit noted, the EA predicts
that the Navy’s “use of MFA sonar in the SOCAL exercises
will result in 564 instances of physical injury including per
manent hearing loss (Level A harassment) and nearly
170,000 behavioral disturbances (Level B harassment), more
than 8,000 of which would also involve temporary hearing
loss.” 518 F. 3d, at 696; see App. 223–224. Within those
totals,
“the EA predicts 436 Level A harassments of Cuvier’s
beaked whales. According to [the National Oceanic and
Atmospheric Administration (NOAA)], as few as 1,121
. . . may exist in California, Oregon and Washington
combined. Likewise, the EA predicts 1,092 Level B
harassments of bottlenose dolphins, of which only 5,271
may exist in the California Coastal and Offshore stocks.”
518 F. 3d, at 691–692.
The majority acknowledges the lower courts’ findings,
ante, at 19, but also states that the EA predicted “only eight
Level A harassments of common dolphins each year” and
“274 Level B harassments of beaked whales per year, none of
which would result in permanent injury,” ante, at 16. Those
numbers do not fully capture the EA’s predictions.

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The EA classified the harassments of beaked whales as
Level A, not Level B. The EA does indeed state that “mod
eling predicts non-injurious Level B exposures.” App. 185.
But, as the majority correctly notes, ante, at 16, the EA also
states that “all beaked whale exposures are counted as Level
A,” App. 185. The EA counted the predicted exposures as
Level A “[b]y Navy policy developed in conjunction with
NMFS.” Id., at 200. The record reflects “the known sensi
tivity of these species to tactical sonar,” id., at 365 (NOAA
letter), and as the majority acknowledges, beaked whales are
difficult to study, ante, at 16. Further, as the Ninth Circuit
noted, “the EA . . . maintained that the methodology used
was based on the ‘best available science.’ ” 518 F. 3d, at
669.4
In my view, this likely harm—170,000 behavioral disturb
ances, including 8,000 instances of temporary hearing loss;
and 564 Level A harms, including 436 injuries to a beaked
whale population numbering only 1,121—cannot be lightly
dismissed, even in the face of an alleged risk to the effective
ness of the Navy’s 14 training exercises. There is no doubt
that the training exercises serve critical interests. But
those interests do not authorize the Navy to violate a statu
tory command, especially when recourse to the Legislature
remains open. “Of course, military interests do not always
trump other considerations, and we have not held that they
do.” Ante, at 26.
In light of the likely, substantial harm to the environment,
NRDC’s almost inevitable success on the merits of its claim
4 The majority reasons that the environmental harm deserves less
weight because the training exercises “have been taking place in SOCAL
for the last 40 years,” such that “this is not a case in which the defendant
is conducting a new type of activity with completely unknown effects on
the environment.” Ante, at 23. But the EA explains that the proposed
action is not a continuation of the “status quo training.” App. 128. In
stead, the EA is based on the Navy’s proposal to employ a “surge” training
strategy, ibid., in which the commander “would have the option to conduct
two concurrent major range events,” id., at 124.

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54 WINTER v. NATURAL RESOURCES DEFENSE
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that NEPA required the Navy to prepare an EIS, the history
of this litigation, and the public interest, I cannot agree that
the mitigation measures the District Court imposed signal
an abuse of discretion. Cf. Amoco Production Co. v. Gam
bell, 480 U. S. 531, 545 (1987) (“Environmental injury, by its
nature, can seldom be adequately remedied by money dam
ages and is often permanent or at least of long duration, i. e.,
irreparable. If such injury is sufficiently likely, therefore,
the balance of harms will usually favor the issuance of an
injunction to protect the environment.”).
For the reasons stated, I would affirm the judgment of the
Ninth Circuit.