Kriegsmarine

The Reichsmarine, later called Kriegsmarine (, "War Navy") was the Navy of Weimar Republic from 1919 to 1935 and Nazi Germany from 1935 to 1945. It replaced the Imperial German Navy of World War I and the inter-war "Reichsmarine". The "Kriegsmarine" was one of three official branches of the "Wehrmacht", the armed forces of Nazi Germany.
History.
The "Kriegsmarine" was developed during the German naval rearmament of the 1930s. The Treaty of Versailles had limited the size of the German navy after World War I. It also prevented Germany from building submarines. But by 1934 Germany had secretly most of the parts they needed to construct submarines (called U-boats). In early 1935 Hitler ordered the U-boats to be built. In January 1939 Plan Z was ordered, calling for the construction of many surface naval vessels. The ships of the "Kriegsmarine" fought during the Spanish Civil War and World War II. The commander of the "Kriegsmarine" was Karl Dönitz.
Ships.
The Kriegsmarine's most famous ships were the U-boats. Most of them were built after Plan Z was abandoned at the beginning of World War II. Wolfpacks were groups of submarines that attacked British convoys. Most of the attacks were during the first half of the Battle of the Atlantic. Along with the U-boats, commerce raiders and cruisers were used to disrupt Allied shipping in the early years of the war. The most famous of these were the heavy cruisers "Admiral Graf Spee" and "Admiral Scheer" and the battleship "Bismarck". However, the allied adoption of convoy escorts greatly reduced the danger from commerce raiders.