The Kriegsmarine was the name of the German Navy during theNazi regime (1935–1945). It superseded the Reichsmarine and the Kaiserliche Marine of World War I. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.
The Kriegsmarine's most famous ships were the U-boat wolf packs, constructed after Plan Z was abandoned on the eve of World War II.
Throughout the war, many US news papers reported on the staggering losses US shipping was taking from U-Boats of the Kriegsmarine. They were angered and frustrated that the US Navy and the Roosevelt administration seemed powerless to not only prevent these losses but sink the U-Boats plaguing the waters of the US East Coast.
When war broke out in 1938, the Kriegsmarine could do very little except sinking British frigate ships in the North Atlantic and fighting Russian ships in the Baltic.
In mid-1939, the Kriegsmarine had it's biggest challenge, when they were used to support the German invasion of Norway. As the land campaign progressed in favour of the Germans, it became clear that their surface ships simply weren't a match for the Royal Navy. Although their battle cruisers managed to sink a few destroyers and a carrier, they suffered heavy losses, which they could not afford to let happen again. In spite of those set backs, the Kriegsmarine dominated the waters of the eastern North Sea.
After the 'Big Switch' in mid 1940, the Kriegsmarine concentrated all of their efforts in the Baltic Sea against the Soviet Navy, while the Royal Navy concentrated on the Barents sea. However, they were unable to break through and get at the Soviet Fleet, due to sea mines and aircraft.
After the British Coup, the Kriegsmarine began conducting U-Boat operations out of Norway, attempting to prevent the BEF from returning to England.