The world's first practical submarine was built in 1620 by Dutch engineer Cornelis Jacobszoon Drebbel, under the patronage of James 1 of England. Drebbel built three submarines according to the sketchy information available from that time, each larger than the last and the third being capable of carrying 16 people, of which 12 were the oarsmen. The oarsmen rowed one oar each, with the oars protruding from the side of the boat through waterproofed leather seals. Air was supplied by snorkel-like tubes that were held above the water's surface by floatation devices, enabling the submarine to be underwater for long periods. Accounts suggest the boat could travel from Westminster to Greewich and back under water, completing the return journey in three hours at a depth around 15 feet below the surface.