U.S. Navy plans to test sonar and conduct training in the Atlantic Ocean would cause \"unprecedented harm\" to whales and dolphins, environmentalists say. Twenty environmental groups filed a letter this week opposing the Navy\'s proposed use of sonar and live-fire training for new destroyers, submarines and other warships off Fort Lauderdale, Fla., and elsewhere in the Atlantic, saying it will deafen marine mammals, entangle them in cables and raise the risk of mass strandings, the South Florida Sun Sentinel reported. Training activities could cause more than 2.25 million cases of temporary hearing loss among marine mammals, more than 10,000 cases of permanent hearing loss, nearly 6,000 lung injuries and more than 800 deaths, the Natural Resources Defense Council, Sierra Club, Defenders of Wildlife and other groups said. Jene Nissen, project manager for the Navy\'s environmental impact statement, said that while the Navy has planned procedures to minimize the danger to marine mammals, the training and testing are vital. \"I can\'t emphasize enough how important it is that we provide the sailors the training they need, and we test the equipment and make sure it does work,\" he said. The environmental groups, while acknowledging the need for testing and training, said the Navy should do more to reduce the impact on marine mammals and their habitats.