On June 6, 1944, the Allies launched the biggest armada in history to invade the Normandy beaches and liberate Europe from the Nazis. Now, NOVA has exclusive access to the first complete survey of the seabed bordering the legendary beachheads. D-Day's Sunken Secrets unfolds an account of the tumultuous events and reveals how the Allies' intricate planning and advanced technology was vital to the ambitious and risky military operation.