The Navy has settled a lawsuit filed by environmentalists challenging its use of sonar in hundreds of submarine-hunting exercises around the world.

The Navy said Saturday the deal reached with the Natural Resources Defense Council and other groups requires it to continue to research how sonar affects whales and other marine mammals.

It doesn't require sailors to adopt additional measures to protect the animals when they use sonar.

The agreement comes one month after the U.S. Supreme Court ruled in favor of the Navy in another sonar lawsuit the NRDC filed.

"The Navy is pleased that after more than three years of extensive litigation, this matter has been brought to an end on favorable terms," Frank R. Jimenez, the Navy's general counsel, said in a statement.

NRDC officials could not immediately be reached for comment. The plaintiffs asked the judge to dismiss the case on Friday.

The NRDC and five other plaintiffs filed the lawsuit in federal court in the Central District of California on October 19, 2005.

The complaint sought a court order to curb mid-frequency sonar, the Navy's preferred method for detecting enemy submarines, on the grounds the sonar disturbs and sometimes kills whales and dolphins.