Washington ? The Defense Department granted the Navy a national security exemption Friday to use sonar during maritime exercises off both coasts for the next six months, letting the service sidestep a lawsuit that sought to protect whales near Hawaii from the noise.

Environmental groups sued the federal government Wednesday to prevent the Navy from using sonar during maritime exercises off Hawaii, saying the sound could harm whales and other marine mammals. One portion of their lawsuit still is pending.

The exercise began this week, but the sonar portion of it will not begin until after Tuesday, the Navy has said.

The six-month exemption would allow the exercise to continue without a permit from U.S. regulators. And it will exempt the Navy from any requirements of the Marine Mammal Protection Act for that time.