A judge has ruled that the US Navy must adhere to a curb on the use of strong sonar in waters off California, amid concerns about its effect on whales.
Campaigners say strong sonar can injure whales and cause stranding
Judge Florence-Marie Cooper overturned an exemption granted last month by President George W Bush.
He had cited national security when he ordered the Navy's submarine detection exercises should go on.
Conservationists hailed the judge's ruling. It is the latest in a series of disputes over the Navy's use of sonar.
Environmental campaign groups led by the Natural Resources Defense Council (NRCD) say whale strandings and deaths are associated with sonar blasts, which are also thought to damage the brains and ears of marine mammals.
Judge Cooper ruled that there was no reason to exempt the navy from a court injunction barring the use of powerful submarine-detecting radar in a 12-mile zone off southern California, which is a habitat for dolphins, whales and other animals.
The injunction stipulates that all sonar be switched off if marine mammals are spotted within 2,200 yards (2,012m).
The judge also expressed "significant concerns" about the constitutionality of President Bush's exemption.
"It's an excellent decision," NRDC attorney Joel Reynolds told The Associated Press news agency.
"It reinstates the proper balance between national security and environmental protection."
But White House spokesman Tony Fratto said the administration disagreed with the judge's decision.
"We believe the orders are legal and appropriate," he said, according to AP.
When he signed a waiver on the injunction on 15 January, President Bush said it would "undermine the Navy's ability to conduct realistic training exercises".