Throughout the 1970s and 80s, the front line of the Cold War was hidden beneath the ocean. Submariners from three navies - American, Soviet and British - played a deadly game of cat and mouse in a secret war of espionage and intimidation. The nuclear balance between East and West was constantly shifting. This was a constant struggle to gain technological advantage, and the Soviets developed submarines that were ever more sophisticated - bigger, faster and more luxurious - than any developed by the West. For over 40 years the details of this tense stand-off have been a closely guarded secret. Now submariners from all three navies are able to talk more openly than ever before. They reveal how the underwater arms race took ballistic missiles beneath the Arctic ice, and they remember how it nearly ended in nuclear disaster at sea.