An Appeals Court in California has found a 2012 decision - to allow naval use of low-frequency sonar for training, testing, and operations - was contrary to the US Marine Mammal Protection Act, which states peacetime oceanic programmes must have "the least practicable adverse impact on marine mammals."
Environmentalists have claimed 155 whales and dolphins in certain parts of Southern California and the Hawaiian islands were killed by the US Navy's mid-frequency active sonar and explosives, with estimates for serious injuries in the range of 2,000.
The use of sonar has been shown to cause whales to swim hundreds of miles to escape, change depth so fast that injury is caused, or beach themselves in order to avoid rolling walls of noise that're nearly twice the volume of the loudest rock concert.
This lawsuit by the Natural Resources Defence Council is part of a larger campaign to limit man-made oceanic noises impacting the health, feeding, and breeding patterns for marine mammals. Other examples include sounds caused by shipping vessels and seismic oil and gas drilling.