Aimed at young readers, the book surveys the development of undersea craft from early experimental designs to contemporary types and explains how submarines are built, controlled, and operated. It provides practical instructions and diagrams for constructing and running model submarines and torpedoes, and describes hull structure, ballast and diving systems, power plants (gasoline and electric), periscopes, armament, mines, signaling methods, and crew accommodations. Detailed chapters address torpedo construction and launching, submarine armament and defenses, and electronic and optical sensing, while photographs and drawings illustrate mechanisms and encourage hands-on learning about submarine technology and its role in modern naval conflict.