A detailed account of submarine warfare during the First World War that traces the technical development and operational use of underwater craft, particularly by the Royal Navy, alongside the rise of German U-boats. It blends action-focused narratives of patrols, attacks, accidents, and anti-submarine measures such as depth-charge tactics and blockades, with analyses of strategic effects in theatres including the Dardanelles and the Baltic. The prose highlights the everyday hazards faced by crews, examples of daring and loss, and the interaction between submarines and surface forces, concluding with the containment of enemy bases and the eventual collapse of hostile naval efforts.