This book examines the operational history of the 29th Unterseebootsflottille, the German Kriegsmarine unit tasked with conducting submarine warfare in the Mediterranean between December 1941 and September 1944, as well as, in part, the history of the 23rd U-Boat Flotilla (23. Unterseebootsflottille), which was also active in the Mediterranean (1941-1942) and was based in Salamis, Greece, under the command of Kapit nleutnant Fritz Frauenheim. Through an analysis of its formation, command structures, major military operations, and gradual decline in the face of Allied air and naval supremacy, this essay reconstructs the contribution-and the strategic limitations-of this unit in one of the secondary theaters of World War II, demonstrating how the Mediterranean represented an operational environment for U-boats that was radically different from the Atlantic, and ultimately insurmountably hostile.