On April 10, 1963, the nuclear-powered killer sub Thresher, on a test dive off the Maine Continental shelf, encountered an as yet unspecified disaster and sank with 12 officers, 96 enlisted men and 21 ""observers"" aboard. It was the worst submarine loss in history. Even today the Navy keeps under wraps much so-called classified information that might lead to some kind of voracious explanation of the grim mystery. John Bentley has birddogged this story for almost a decade and, despite the Navy's abysmal uncooperativeness, has become perhaps the most knowledgeable man alive about the lost sub. His story includes a realistic ""dramatization"" (with dialogue) of the sub's fatal operation and last moments, with some educated guesses about the possible causes of the accident. For one, the sub put to sea before it was 100 per cent ready after a long overhaul in dry dock. The climactic implosion-explosion, which blew the Thresher over 140,000 square yards, is rendered with hair-raising immediacy. The book also features a long interview with an officer who was ordered ashore on the last day before sailing, and it reviews what few records the Navy finally released. This is an angry book and hopefully it will spur a new look into declassified ""secrets.