Only one word describes the secrets revealed in this video: astonishing. For 40 years, submarine crews lived on the front lines of the Cold War, but until recently few knew the hidden history of their tragedies and triumphs. Through candid interviews with Soviet and US military personnel, shocking underwater footage, and recently de-classified film and documents, NOVA lifts the veil on deadly, mysterious submarine accidents and high-risk spy missions.

Hear famed underwater explorer Bob Ballard detail his secret search missions. Find out what sank the "killer shark" Thresher, the Navy's most advanced nuclear submarine. See the USS Scorpion lying at 10,000 feet and join investigative journalists uncovering new evidence that contradicts official Navy statements. Understand how the ultra-high-tech recovery of a sunken Soviet sub in 1968 became the largest covert operation since the Manhattan Project, and learn how the mission's cover (as Howard Hughes' deep-sea mining operation) duped America... and even NOVA.