KITTERY, Maine (AP) - Those who lost loved ones in the deadliest submarine disaster in U.S. history are preparing for an emotional 50th anniversary. There are weekend events in Portsmouth, N.H., and Kittery, Maine, to memorialize the nuclear-powered submarine USS Thresher, which sank with the loss of 129 lives about 220 miles off Cape Cod on April 10, 1963. The Navy believes a leak in a pipe shorted out an electrical panel, leading to a cascading series of events that caused the destruction of the sub, now on the sea floor 8,500 feet deep. Part of the Thresher's legacy is safety. Vice Adm. Kevin McCoy, commander of the Naval Sea Systems Command in Washington, D.C., says, "We can never, ever let this happen again."