The submarine was the invisible but formidable weapon of the Royal Navy during World War II. This book examines the three major classes – ''S'', ''T'' and ''U'' – detailing their design, development and modification.

The major submarine engagements of the war are recounted, including the Norwegian campaign, the battle of Malta in March 1942, Operation Pedestal, and many other engagements in all theatres between the British subs, German U-Boats and Japanese subs.

Using many previously unpublished sources and his own extensive underwater explorations, Innes McCartney gives a highly detailed account of the British submarine.