WASHINGTON  —  The Defense Department granted the Navy a national security exemption Friday, effectively sidestepping a lawsuit that could have prevented the use of sonar during a maritime exercise that began this week.

Environmental groups sued the federal government on Wednesday to prevent the Navy from using sonar during maritime exercises off Hawaii, saying the sound could harm whales and other marine mammals.

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 will allow the exercise to continue without a permit from U.S. regulators.