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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 155 (“a preliminary injunction will not be issued simply to prevent the possibility of some remote future injury”). Issuing a preliminary injunction based only on a possibility of ir-reparable harm is inconsistent 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 affected the Ninth Circuit’s analysis of irreparable harm. Although the court referred to the “possibility” standard, and cited Circuit precedent along the same lines, it af-firmed 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 originally 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 imposed by the court. See supra, at 7–8. 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-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 completely 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). In-stead, 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 significant environmental impacts.” Id., at 349. Part of the harm NEPA attempts to prevent in requiring an EIS is that, without one, there may be little ifany information about prospective 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 defendant 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 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 __ (slip op., at 12). 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 remedy 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 decisions as to the composition, training, equipping, and control of a military force,” which are “essentially professional military 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.” Boumediene v. Bush, 553 U. S. __, __ (2008) (slip op., at 68). 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 ex Gary Roughead—the Chief of Naval Operations—stated that during training exercises:
“It is important to stress the ship crews in all dimensions of warfare simultaneously. If one of these training 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 described the ability to operate MFA sonar as a “highly perishable 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 coordinate 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 challenged 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 surface 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 submitted declarations asserting that they take whale watching trips, observe marine mammals underwater, conduct scientific research on marine mammals, and photograph these animals 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 interests, we conclude that the balance of equities and consideration 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 antisubmarine force jeopardizes the safety of the fleet. Active sonar is the only reliable technology for detecting and tracking enemy diesel-electric submarines, and the President—the Commander in Chief—has deter-mined that training with active sonar is “essential to national security.” Pet. App. 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 interests 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 equities and the public interest in determining whether to grant a preliminary injunction, the District Court ad-dressed 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 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 previous 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 discretion, 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 impose 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 injunctive relief to alter a defendant’s conduct. The lower courts failed properly to defer to senior Navy officers’ specific, predictive judgments about how the preliminary injunction would reduce the effectiveness of the Navy’s SOCAL training exercises. See Wright & Miller §2948.2, at 167–68 (“The policy against the imposition of judicial restraints prior to an adjudication of the merits becomes more significant when there is reason to believe that the decree will be burdensome”).

2. The preliminary injunction requires the Navy to shutdown 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 during training exercises are relatively rare. But regardless of the frequency of marine mammal sightings, the injunction will greatly increase the size of the shutdown zone. Pursuant to its exemption from then 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 = p r2). Increasing the radius of the shutdown zone from200 to 2,200 yards would accordingly expand the surface area of the shutdown zone by a factor of over 100 (from125,664 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 because 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. Admiral Bird explained that the 2,200-yard shutdown zone would cause operational commanders 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 sighting, the preliminary in-junction would clearly increase the number of disruptive sonar shutdowns the Navy is forced to perform during its SOCAL training exercises.
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