The 200-year evolution of the submarine in wartime is examined, told by the designers and engineers behind the machines. This episode begins with the story of HMS Conqueror sinking the ARA General Belgrano during the Falklands War. Then the beginnings of submarines – the Turtle in the War of Independence, and the Civil War craft the Hunley. Resurgam was a Victorian submarine that sank off the Welsh coast. We tell the story of Charles Fryatt who used his ferry to ram a U-Boat rather than surrender. We explore the US submarine Becuna and the story of the giant I-400 Japanese subs. A crewmember from the USS Nautilus describes what it was like to serve on the world's first nuclear submarine.