British mathematician William Bourne made some of the earliest known plans for a submarine around 1578, but the world’s first working prototype was built in the 17th century by Cornelius Drebbel, a Dutch polymath and inventor in the employ of the British King James I. Drebbel’s sub was probably a modified rowboat coated in greased leather and manned by a team of oarsmen. Sometime around 1620, he used it to dive 15 feet beneath the River Thames during a demonstration witnessed by King James and thousands of astonished Londoners. Unfortunately, none of Drebbel’s plans or engineering drawings has survived to today, so historians can only guess about how his “diving boat” actually operated. Some accounts say it submerged via a collection of bladders or wooden ballast tanks, while others suggest that a sloping bow and a system of weights were used to propel the boat underwater when it was rowed at full speed.
