For the second half of the 20th century, the world’s most powerful nations were engaged in an intense struggle for political and territorial supremacy. As the USA and the USSR developed huge arsenals of nuclear weapons, they and their allies would regularly bring the world close to annihilation, yet – incredibly – these highly dangerous military stand-offs often happened in total secrecy: underwater. This eye-opening documentary from the BBC tells the compelling story of US, UK and Russian submarine warfare and the espionage operations that took the world to the brink of nuclear war.