The U.S. Supreme Court has overturned a lower court ruling that restricted the Navy’s use of sonar during training exercises to protect marine wildlife from its potential adverse effects. With the high court’s Nov. 12 decision, Navy vessels will no longer have to shut down mid-frequency active sonar units whenever marine mammals are detected within 2,200 yards, or power down to six decibels during certain surface exercises. A federal district court in California had imposed the restrictions in response to a lawsuit filed against the Navy by the Natural Resources Defense Council, an environmental group. After the U.S. Court of Appeals for the 9th Circuit upheld that ruling, the Navy appealed to the Supreme Court, which heard oral arguments on Oct. 8. Writing the majority opinion, Chief Justice John Roberts noted that the environmental group acknowledged there is no direct proof that sonar use harmed marine animals. "We do not discount the importance of [the environmentalists’] ecological, scientific, and recreational interests in marine mammals," Roberts wrote. "Those interests, however, are plainly outweighed by the Navy’s need to conduct realistic training exercises to ensure that it is able to neutralize the threat posed by enemy submarines."