The super submarine leaves Chatham Dreadnought of the under seas HM Submarine X1 was conceived and designed as a submersible commerce raider for the Royal Navy; at the time of her launching she was the largest submarine in the world . She displaces 3 , 000 tons and Unde water 3 , 500 tons and can be turned in her own length , 350 feet . Her fore turret can be seen with a crewman heaaving the lead 12 September 1925