Environmental groups are suing the Navy, arguing that sonar used in routine training and testing violates environmental laws. They say the Navy's sonar injures and kills marine mammals, including whales and dolphins, and that the Navy fails to take precautions that could spare animals from death.

Animal welfare organizations have documented cases of mass whale strandings and deaths around the world that they say are associated with sonar blasts thought to disorient marine mammals and can cause bleeding from the eyes and ears.

The Navy says it has rigid standards and measures in place to protect marine mammals, such as stationing trained look-outs for marine mammals on vessels conducting the exercises and listening for marine mammals in the area.

The exemption removes one legal avenue for environmental groups to challenge the Navy's use of sonar. Those groups still may sue the Navy under two other environmental laws -- the National Environmental Policy Act and the Endangered Species Act, the Navy said.

"The rule in this country has always been that no one is above the law, including the military," said Richard Kendall, an attorney at Los Angeles law firm of Irell & Manella and co-counsel for plaintiffs in an outstanding lawsuit.

"We intend to continue our efforts to force the Navy to mitigate its sonar use by prosecuting the Navy's other violations of law," he said.

Navy Deputy Assistant Secretary Don Schregardus said the exemption was needed so that training may continue.

"We've asked for this exemption so that we can comply with the law and continue training while we are developing the long-term documentation for our major ranges and training areas," he said.

Without the exemption, the Defense Department would need to complete full environmental impact studies and receive letters of authorization for each exercise -- a process that could take six months to two years to complete, Schregardus said.

"There's just no way we could do it" in that time period, he said.