On April 10, 1963, the USS Thresher, the lead ship of a new class of nuclear-powered attack submarines, was conducting sea trials off the coast of New England with another ship, the USS Skylark (ASR-20). The two ships were in communication by means of underwater sound telephone. At 0747 the USS Thresher started a deep dive. Everything was fine until 0913. At this time the USS Thresher sent this message. 