A group of men is seen as the film opens asking General Von Hindenberg to name the man who more than any other was responsible for Germany's World War defeat. Much to their surprise he names David Bushnell, an American Colonial inventor who built the first submarine and the depth bomb which was successful in combating it in the war. Bushnell is shown in his crude physics laboratory experimenting with the explosion of powder under water. The primitive submarine built by him during the Revolutionary War to destroy wooden frigates is shown in action against the English fleet. The remainder of the picture presents the "Ash Can Fleet", the wooden boats developed during the World War to attack submarines with "depth bombs.