HONOLULU -- The Defense Department exempted the Navy on Tuesday from complying with the Marine Mammal Protection Act for the next two years so sailors can practice tracking submarines with sonar.

Environmentalists swiftly denounced the move, saying the Navy wasn't doing enough to protect whales, dolphins and other marine mammals from the harmful effects of the underwater sound technology.

Navy officials said they need the exemption, allowed for under the 2004 National Defense Authorization Act, to give them enough time to conduct environmental impact statements for sonar use at major underwater training ranges.

The studies required by the Marine Mammal Protect Act will take about two years to complete, Navy officials said.

The ranges are off Hawaii, Southern California and the East Coast.