After the National Resources Defense Council made their pitch in court, a judge issued a temporary injunction against the Navy.  The judge found that NRDC had shown "considerable convincing scientific evidence" showing that military sonar can harm marine animals.

As a result, the Navy has agreed not to use mid-frequency sonar during training within a 25-mile buffer zone surrounding the Northwestern Hawaiian Islands Marine National Monument, an area rich in marine life, in a settlement with the National Resources Defense Council and other groups.

The settlement, reached Friday in U.S. District Court in Los Angeles, also calls for the Navy to post lookouts for whales and other marine mammals during the exercises and report sightings, after which the Navy is required to reduce the intensity of the sonar or stop it.

The agreement comes on the heels of a temporary restraining order won Monday by environmental groups preventing the Navy from using a type of high-intensity sonar during the "Rim of the Pacific," or RIMPAC, 2006 anti-submarine warfare training exercise.

"The value of this settlement is that it increases significantly the protection for whales and dolphins and other marine life during this RIMPAC exercise," NRDC spokesman Daniel Hinerfeld said.

"By agreeing to these measures, the Navy has implicitly acknowledged that taking better care of the oceans and marine life is compatible with their need to train with sonar."

The military exercise involving eight countries and more than 40 ships, six submarines, 160 aircraft and thousands of military personnel concludes July 28. The Navy claims that training sailors to detect submarines using mid-frequency active sonar is crucial to military operations in the Pacific.

"The Navy will continue to use all possible mitigation measures to protect marine mammals, yet provide realistic and necessary training," Vice Adm. Barry Costello, commander of the RIMPAC exercises, wrote.

"Effective use of active sonar is a vital and perishable skill set that must be continually practiced," he added, calling anti-submarine warfare the top priority for the U.S. Pacific Fleet Commander.

Environmentalists have documented dozens of cases of mass whale strandings and deaths around the world they say are associated with sonar blasts, which are thought to disorient marine mammals and can cause bleeding around the brain and internal injuries. A U.N. Environment Program report issued in November included underwater sonar and military manoeuvres in a list of threats to marine mammals.

The NRDC’s Hinerfeld said sonar was to blame for a mass stranding of 150 whales during the 2004 RIMPAC.

Friday’s settlement does not stop a separate lawsuit that challenges the Navy’s overall use of sonar.