A number of empty tanks were so fixed in the vessel that when the pilot wanted to submerge it he could let the water into them, and when he wanted to rise to the surface again he could pump the water out with a hand force-pump. This scheme is used in all of the submarine boats of the present time, though of course the pumps are power-driven.
A heavy weight that could be detached was fixed to the bottom of the craft, which helped it to maintain its upright position and also aided in submerging it. In case an accident happened to the pumps the weight could be released, when the craft would come to the surface.
Another good feature of this submarine was the valves which let fresh air into the vessel when it floated on top of the water but which closed automatically—that is, without the help of the pilot—when the submarine sank below the water line.
The way the first submarine of Bushnells was driven was just as primitive as the one built by Van Drebel; indeed, it was a shade worse, for a solitary oar sticking through the rear end of the shell provided the means for going ahead while another oar on one side helped to raise and lower it.
He later designed, built, and successfully operated another submarine, which was far superior to his first model. It had the same shape as his first one but it was propelled by two screws which were turned by hand; one of these moved the submarine forward and backward through the water, and the other one moved it up and down—all of which is clearly shown in [Fig. 4]. Hence the credit for the invention of the screw-driven submarine belongs to Bushnell.
The First Torpedo Fired by a Submarine.—Bushnell, though, did more than to invent a workable submarine, for he also devised and used a torpedo; or it would be better to call it a bomb, since it was timed to explode by clock-work, instead of by concussion. He intended to hang this submarine bomb on the bottom of an enemy ship—and thereby hangs a tale.
The British man-of-war Eagle had anchored in New York Harbor close to Staten Island sometime in the famous year of 1776.
The inventor was a patriot and offered his services and the use of his submarine to the new United States Government; the latter accepted them and ordered him to blow up the warship. As the inventor became sick he gave a sergeant, named Lee, the honor of using his submarine and blowing up the ship. Lee worked the submarine without a hitch until he reached the man-of-war, and then his troubles began.