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SUPREME COURT OF THE UNITED STATES
No. 07–1239

DONALD C. WINTER, SECRETARY OF THE NAVY,
ET AL., PETITIONERS v. NATURAL RESOURCES
DEFENSE COUNCIL, INC., ET AL.

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
APPEALS FOR THE NINTH CIRCUIT
[November 12, 2008]

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 Presidents 57 (J. Richardson comp. 1897). So said George Washington 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 detect and track enemy submarines, something the Navy has done for the past 40 years. The plaintiffs complained that the Navy’s sonar training pro-gram 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 upheld 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. (Pet. App.) 316a–317a. Seam-less coordination among strike-group assets is critical. Before deploying a strike group, the Navy requires extensive integrated training in analysis and prioritization of threats, execution of military missions, and maintenance of force protection. App. 110–111.Antisubmarine warfare is currently the Pacific Fleet’ stop 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 extremely difficult to detect and track. Potential adversaries of the United States possess at least 300 of these submarines. App. 571. The most effective technology for identifying submerged diesel-electric submarines within their torpedo range is active sonar, which involves emitting pulses of sound underwater and then receiving the acoustic waves that echo off the target. Pet. App. 266a–267a, 274a. Active sonar is a particularly 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 quieter 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 contours of the sea floor. Id., at 278a–279a. When working as part of a strike group, sonar operators must be able to coordinate with other Navy ships and planes while avoiding interference. 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 exercises, as this is the only area on the west coast that is relatively close to land, air, and sea bases, as well as amphibious 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, submarines, 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 warfare. Accordingly, the SOCAL exercises include extensive training in detecting, tracking, and neutralizing enemy submarines. 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 extent to which the Navy’s training activities will harm those animals or disrupt their behavioral patterns. The Navy emphasizes that it has used MFA sonar during training exercises in SOCAL for 40 years, without a single documented sonar-related injury to any marine mammal. The Navy asserts 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, Jean-Michael Cousteau (an environmental enthusiast and filmmaker), and several other groups devoted to the protection of marine mammals and ocean habitats. They contend 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 stranding of marine mammals (outside of SOCAL) 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 active sonar; these injuries would not necessarily be detected by the Navy, given that beaked whales are “very deep divers” 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 Secretary 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 officers 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 aircraftand 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 transmission 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 ex-tent possible” to prepare an environmental impact statement (EIS) for “every . . . major Federal actio[n] significantly affecting the quality of the human environment.” 42 U. S. C. §4332(2)(C) (2000 ed.). An agency is not required to prepare a full EIS if it determines—based on a shorter environmental assessment (EA)—that the pro-posed 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 temporary injury or disruption of behavioral patterns such as migration, 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 harassments of common dolphins each year, and that even these injuries could be avoided through the Navy’s voluntary mitigation 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 deter-mined that it was unnecessary to prepare a full EIS. See 40 CFR §1508.13.
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