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.
[Illustration: FIG. 4. BUSHNELL’S SUBMARINE.]
=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.
Try as he would, he could not drive the screw into the tough English oak of which the hull of the ship was made, and this he must needs do in order to fasten the bomb to the bottom of it.