## Facts

- The U.S. Navy planned 14 integrated strike-group training exercises off Southern California using mid-frequency active (MFA) sonar to certify antisubmarine warfare readiness.
- The area contained numerous marine mammal species; environmental organizations alleged MFA sonar could injure marine mammals and disrupt behavior.
- The Navy disputed the asserted level of risk and emphasized decades of training in the area without documented sonar-related marine mammal injury, along with existing mitigation practices.
- Environmental organizations sued under NEPA, contending the Navy was required to prepare an Environmental Impact Statement before proceeding.
- The district court granted a preliminary injunction; after appellate review, it imposed restrictions including (1) sonar shutdown when a marine mammal was spotted within 2,200 yards and (2) a mandatory 6-decibel power-down during “surface ducting.”
- The Ninth Circuit affirmed the modified injunction.
- Separately, the Council on Environmental Quality authorized alternative NEPA compliance arrangements due to emergency circumstances, and the President exempted the exercises from certain Coastal Zone Management Act requirements.

## Issues

1. Whether a plaintiff seeking a preliminary injunction must show irreparable harm is likely absent an injunction, rather than merely possible.
2. Whether the balance of equities and the public interest justified judicial restrictions on Navy sonar training in light of asserted environmental harms and asserted national security and readiness harms.
3. Whether the lower courts properly tailored preliminary injunctive relief as a remedy for the alleged NEPA violation.

## Decision

- The Supreme Court vacated the preliminary injunction and reversed the Ninth Circuit.
- The Court held the lower courts applied an improperly lenient irreparable-harm standard by allowing relief based on a “possibility” of irreparable harm.
- The Court concluded the balance of equities and the public interest favored allowing the training to proceed under the Navy’s mitigation measures rather than under court-imposed restrictions.

## Legal Principles

- A preliminary injunction requires a plaintiff to establish: (1) likelihood of success on the merits, (2) likelihood of irreparable harm absent preliminary relief, (3) equities favoring the plaintiff, and (4) that an injunction is in the public interest.
- A “possibility” of irreparable harm is insufficient; irreparable injury must be likely.
- Courts must weigh competing public interests in the injunction analysis, and they must give substantial deference to military judgments about training and readiness when assessing equities and public interest.
- Even where a NEPA procedural violation is alleged, injunctive relief is not automatic; it must satisfy the traditional four-factor test and be justified by the record.

## Conclusion

The Court held that preliminary injunctive relief restricting naval training could not rest on a merely possible risk of irreparable environmental harm and that, on this record, the equities and public interest in effective military readiness outweighed the asserted harms from sonar use, requiring vacatur of the injunction.


Winter v. Nat. Res. Def. Council, Inc., 555 U.S. 7 (2008)