At the height of the Cold War, US subs gathered secrets that neither spies nor satellites could expose. Until recently, almost nobody knew the hidden history of their tragedies and triumphs. As the US strove for supremacy in the Cold War, it pushed submarine technology to its limits. Breakthroughs led to unparalleled triumphs of espionage. And, missteps cost hundreds their lives. With recently declassified film, NOVA lifts the veil on tragic and mysterious submarine accidents and their high-risk spy missions that helped win the Cold War. Along with celebrated oceanographer and explorer, Robert Ballard (discoverer of the Titanic), NOVA goes in search of clues to two tragedies of the Cold War, the wrecks of the nuclear submarines Thresher and Scorpion. Recently declassified footage gives a unique glimpse of the wrecks and a chance to investigate the catastrophic accidents that overtook these subs and their crew.