The Submarine was designed to be an underwater warship but was kept secret by it's creater Leonardo da Vinci. It was kept secret because da Vinci simpely didn't want war to be any more terrifying then it already was. In 1578 William Borne began drawing plans for his own submarine but it was never built just like da Vinci's but this submarine had tanks to fill up and empty to rise and sink. In 1620 Cornelis Drebbel Built a submarine which was a rowboat with a leather cover and oars with watertight seals. 12 people could ride in this submarine. Drebbel was an engineer who worked for the brittish navy and was the first person to discuss the problem of air repenishment well the the submarine was under water. Though he never solved this probelm his submarine could only go 15 feet underwater and stay under for only a couple hours. In think this is a pretty good invention because it leads to today deep sea exploration.