While at Yale, he proved that gunpowder exploded under water. With this, he also came up with mine barrage in 1777. He also invented the first time bomb. He combined his ideas in an attempt to attack British ships which were blockading New York Harbor in the summer of 1776 by boring through their hulls and implanting time bombs, but failed every time due to a metal lining in the ships hull to protect against parasites in their previous station, the Caribbean. David Bushnell then created the Turtle. The Turtle eventually sank
On June 8, 1781 he was promoted Captain of Sappers and Miners. Bushnell later traveled to France and then settled in Warrenton, Georgia where he taught at the Warrenton Academy and practiced medicine. He died in 1824, but before he died David was honored with a medal by George Washington. David Bushnell's Submarine Model is on display at the U.S. Navy Submarine Force Museum and Library in Groton, Connecticut.