The Rocket U-boat was a series of military projects undertaken by Nazi Germany during the Second World War. The projects, which were undertaken at Peenemünde Army Research Center, aimed to develop submarine-launched rockets, flying bombs and missiles. The Kriegsmarine (German Navy) did not use submarine-launched rockets or missiles from U-boats against targets at sea or ashore. These projects never reached combat readiness before the war ended.
From May 31 to June 5, 1942, a series of underwater-launching experiments of solid-fuel rockets were carried out using submarine U-511 as a launching platform. The rocket system was first envisaged as a weapon against convoy escorts but with no effective guidance system, the arrangement was ineffective against moving targets and could only be used for shore bombardment. Development of this system ended in early 1943 because it decreased the U-boats' seaworthiness.
Plans for the rocket U-boat involved an attack on New York City using newly invented V-2 rockets; Unmanned and unpowered containers with V-2 rockets inside were to be towed within range of the target by a conventional U-boat then set up and launched from its gyro-stabilized platform. With thoughts of hitting targets in the United States and in the United Kingdom, a 32 m (105 ft)-long container of 500-tons displacement was to be towed behind a submerged U-boat. The evacuation of Peenemünde in February 1945 brought an end to these developments. There are no records that these were tested with a rocket launch before Germany's final defeat. It is the forerunner and basis of modern ballistic missile submarines. After the war, the United States and the Soviet Union continued these projects with the assistance of captured German scientists. The US Navy fired Republic-Ford JB-2 flying bombs – reverse engineered versions of the German V-1 flying bomb – from submarines USS Cusk (SS-348) and USS Carbonero (SS-337) in a series of successful tests between 1947 and 1951. During Operation Sandy, a German V-2 rocket seized by the US Army was launched from the upper deck of the aircraft carrier USS Midway (CV-41) on September 6, 1947. In the Soviet Union, German scientists contributed to the development of GOLEM-1, a liquid-fueled rocket based on the V-2 rocket design and designed to be launched from a submarine-towed capsule.