Today is Submarine Day.
The first recorded submarine was built by Cornelis Drebbel in 1620 for the Royal Navy (it wasn't, as the Yanks would have you believe, built by the Yanks to fight the British in the War of Independence), although why anyone would want to plunge beneath the surface of the 17th Century Thames is beyond me.
Using William Bourne's design from 1578, he manufactured a steerable submarine with a leather-covered wooden frame. Between 1620 and 1624 Drebbel successfully built and tested two more submarines, each one bigger than the last. The final (third) model had 6 oars and could carry 16 passengers. This model was demonstrated to King James I (of England) and VI (of Scotland) in person and several thousand Londoners. The submarine stayed submerged for three hours and could travel from Westminster to Greenwich and back, cruising at a depth of from 12 to 15 feet (4 to 5 metres). Drebbel even took James in this submarine on a test dive beneath the Thames, making James I and VI the first monarch to travel underwater. This submarine was tested many times in the Thames, but it couldn't attract enough enthusiasm from the Admiralty and was never used in combat.
Reconstruction of the Drebbel, the world's first submarine, in the London Borough of Richmond upon Thames, south west London