The Kriegsmarine (or "War Navy") was the name of the German Navy between 1935 and 1945, during the Nazi regime, superseding the Reichsmarine.Under the terms of the Treaty of Versailles, Germany was only allowed a minimal navy. When the Nazis came to power in 1933, Hitler soon began to ignore many of the Treaty restrictions and to accelerate German rearmament. The Anglo-German Naval Agreement of 18 June 1935 then allowed Germany to build a navy equivalent to 35% of British surface ship tonnage and 45% of British submarine tonnage; battleships were to be limited to no more than 35,000 tons. Following the 1938 crisis of German demands on Czechoslovakia, Germany abandoned all pretensions of adherence to treaty limitations on its navy.

The so-called Plan Z, the blueprint for the German naval construction program finalized in 1938, envisaged building a navy of about 800 ships over the next eight years (1939-1947), including 10 battleships and battlecruisers, 4 aircraft carriers, 15 armored ships (Panzerschiffe), 5 heavy cruisers, 44 light cruisers, 158 destroyers and torpedo boats, and 249 submarines, along with numerous smaller craft. Personnel strength was planned to rise to over 200,000.

Since the simultaneous and rapid build-up of the German army and airforce demanded substantial effort and resources, the planned naval program was not very far advanced by the time World War II began. Indeed, implementation only began in January 1939 when two H-class battleships were laid down. On 1 September 1939, the navy still had a total personnel strength of only 78,000, and it was not at all ready for a major role in the war. With expectations in Germany of a quick victory by land, Plan Z was essentially shelved and the resources initially targeted for its realization were largely redirected to the construction of U-boats.