The Navy is refusing to detail its sonar use for a federal court in a case involving potential harm to whales, saying the information could jeopardize national security. The Natural Resources Defense Council is suing the Navy to ensure sailors use sonar in a way that doesn't harm whales and other marine mammals. Critics say active sonar, which sailors use by pumping sound through water and listening for objects the sound bounces off of, can strand and even kill marine mammals. A U.S. Congressional Research Service report last year found Navy sonar exercises had been responsible for at least six mass deaths and unusual behavior among whales. Many of the beached or dead animals had damaged hearing organs. In considering the lawsuit, U.S. District Judge Florence-Marie Cooper issued an order for the Navy to submit data for the case on when and where sailors have used sonar since 2003. The Navy said in its new release that it refused to comply citing state secrets privilege. Joel Reynolds, a Natural Resources Defense Council attorney, said he would challenge the Navy's position. This latest invocation of state secret privilege is one more attempt to deprive the public of the information it needs to determine whether the Navy is illegally and needlessly endangering the marine environment," Reynolds said.