The first navigable submarine was publicly tested on the river of Thames in London in the United Kingdom on 12th September 1624. It was built by the Dutch engineer and inventor Cornelis Jacobszoon Drebbel, while he was working for the English Royal Navy.
The steerable submarine, with a leather-covered wooden frame, had 6 oars and could carry 16 passengers, was demonstrated to King James I in person, and thousands of people of London. It submerged into the water of river Thames for three hours, at a depth between 12 and 15 feet (4 to 5 meters) traveling from Westminster to Greenwich, and back.
Drebbel even took King James I in this submarine on a test drive, making him the first monarch to travel underwater.