The Navy and marine wildlife experts are investigating whether the beaching of dozens of dolphins in the Florida Keys followed the use of sonar by a submarine on a training exercise off the coast..... A day before the dolphins swam ashore, the USS Philadelphia had conducted exercises with Navy SEALs off Key West, about 45 miles from Marathon, where the dolphins became stranded.... Navy officials refused to say if the submarine, based at Groton, Conn., used its sonar during the exercise. Some scientists surmise that loud bursts of sonar, which can be heard for miles in the water, may disorient...