How did John P. Holland’s submarine designs improve diving control?

John P. Holland’s submarine designs significantly improved diving control by combining the use of water ballast with horizontal rudders, also known as diving planes. These features allowed for more precise management of the vessel's depth and attitude while submerged.1

In his successful Holland submarine, which was accepted by the U.S. Navy in 1900, these capabilities were further refined. The vessel was equipped with a specialized apparatus designed to take the submarine to a predetermined depth, as well as a separate device that maintained the craft in a level position. By integrating these mechanical controls with the ability to flood ballast tanks for submersion, Holland’s designs overcame the instability issues that plagued many other early underwater craft, such as the French Gymnote, which tended to go out of control during dives.21