Winter v. Natural Resources Defense Council, Inc.,
555 U.S. 7 (2008)

Annotate this Case




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 submarines, which are extremely difficult to detect and track because they can operate almost silently. The most effective tool for identifying submerged 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 aircraft train together as members of a “strike group.” Due to the importance 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 marine mammals and ocean habitats—assert that MFA sonar causes serious 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 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 Council 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 previously 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 “emergency 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 injunction on the Navy’s training exercises was “speculative,” and determined 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. 10–24.

   (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 “possibility” 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. 10–14.

   (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 judgment of military authorities concerning the relative importance of a particular 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 submarines 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 conditions 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 concludes 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. 14–16.

   (c) The lower courts’ justifications for entering the preliminary injunction are not persuasive. Pp. 16–21.

      (1) The District Court did not give serious consideration to the balance of equities and the public interest. The Court of Appeals did consider 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 officers’ specific, predictive judgments about how the preliminary injunction would reduce the effectiveness of the Navy’s SOCAL training exercises. Pp. 16–17.

      (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 the loss of several days’ worth of training. The Court of Appeals also concluded that the shutdown zone would not be overly burdensome because 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 insignificant times. Pp. 18–20.

      (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 distortions to avoid being detected by sonar. The Court of Appeals concluded that the power-down requirement was reasonable because surface 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. 20–21.

      (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 injunction 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. P. 21.

   (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 preparation 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. 21–23.

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 concurring in part and dissenting in part, in which Stevens, J., joined as to Part I. Ginsburg, J., filed a dissenting opinion, in which Souter, J., joined.

Primary Holding

The test for whether a preliminary injunction is appropriate requires determining whether the plaintiff is likely to succeed on the merits, whether the plaintiff is likely to suffer irreparable harm without the injunction, whether the balance of equities and hardships is in the plaintiff's favor, and whether an injunction is in the public interest.


In its training exercises at sea, the U.S. Navy uses modern sonar to detect and follow enemy submarines. This technology, which has been used for 50 years, is based on emitting pulses of sound underwater and then receiving acoustic waves that echo off the target. Although this has been established as the most effective way to identify submerged submarines that are within torpedo range, the use of active sonar arguably harms marine mammals. They may be subject to hearing loss, decompression sickness, and behavioral disruptions when the technology is used. The Secretary of Defense is allowed under the Marine Mammal Protection Act of 1972 to exempt an activity that harms marine mammals if it is deemed necessary for national defense, and the Navy had received such an exception for this case.

Under the National Environmental Policy Act of 1969, moreover, federal agencies must compile an environmental impact statement for any major federal action that significantly affects the quality of the human environment. This requirement may be avoided only if the agency uses a shorter environmental assessment to determine that its proposed action will not have a significant impact on the environment. The Navy believed that this exception to the requirement applied, and it issued an environmental assessment in support of that conclusion. The Natural Resources Defense Council sued the Navy to prevent its use of sonar in training programs. The Council received a preliminary injunction in federal court.



  • John G. Roberts, Jr. (Author)
  • Antonin Scalia
  • Anthony M. Kennedy
  • Clarence Thomas
  • Samuel A. Alito, Jr.

The Ninth Circuit erred in using a possibility standard for the irreparable harm element of the preliminary injunction standard. This element should be more demanding to the point of being likely rather than merely possible. Preliminary injunctions should not be issued lightly but only when there is a clear showing that the plaintiff should receive an injunction. This error was harmless here, however, since both the lower court and the Ninth Circuit found from the record that there would be a near-certainty of irreparable harm, which would meet the heightened standard for this element anyway.

Regarding the other elements of the standard, it is clear that any irreparable harm caused by the training exercises would be trumped by the defendant's interest in effectively training its sailors and the public interest in national defense. The preliminary injunction must be denied on these grounds. Sonar is absolutely critical to preparing for the potential threat posed by enemy submarines, which is a serious hazard to national security. While these activities likely will cause serious harm to the environment and the public's recreational interests, the safety of the entire fleet and the nation are more important in a balance of equities than injuries to marine mammals.

The plaintiffs might prevail when the action is decided on the merits, but even then it would be an abuse of discretion to issue a permanent injunction, for the same reasons that it would be erroneous to issue a preliminary injunction.


  • Ruth Bader Ginsburg (Author)
  • David H. Souter

When it is very likely that a plaintiff will succeed on a claim, the plaintiff should be able to obtain an injunction based on a lesser likelihood of harm. A sliding scale is appropriate when a court is sitting in equity jurisdiction.

Concurrence/Dissent In Part

  • Stephen G. Breyer (Author)
  • John Paul Stevens

Case Commentary

This unusual grant of certiorari for a dispute over a preliminary injunction allowed the Supreme Court to emphasize the importance of the national security interest attached to the Navy's training program. Even if the lower court eventually found on the merits that the Navy had violated a law, it probably could not impose a permanent injunction because of this national security interest.

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