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The Rocket U-boat was an abandoned military project to create the first ballistic missile submarine. It was conceived by Nazi Germany during the Second World War. Plans for the rocket U-boat involved an attack on New York City with newly invented V-2 rockets.
During World War II, several projects were undertaken at Peenemunde to mount rockets on a U-boat.
In 1941 first trials were held, using a Nebelwerfer rocket launcher, mounted on the deck of U-511. Tests were carried out, with successful firings from the surface, and from up to 12 metres underwater without any effect on the missiles' accuracy. The arrangement was envisaged as a weapon against convoy escorts, but with no guidance system the arrangement was largely ineffective.
In 1943 interest in the concept was revived with the advent of the V-1 flying bomb; proposals were made to mount a V-1 and launcher on a U-boat in order to strike targets at a much greater range than the 150 mile (251 km) radius from land-based sites. This proposal foundered on inter-service rivalry, however, as the V-1 was an Air Force (Luftwaffe) project.
In 1943 also, consideration was given to firing the V-2 rocket from a U-boat, with particular thought to hitting targets in the United States. As the V-2 was too large to be mounted on any U-boat then in service, a 500-ton submersible vessel for transport and launching was designed. Un-manned and unpowered, this was intended to be towed by a conventional U-boat to within range of its target, then set up and launched. Three of these vessels were ordered in late 1944, but only one was built, and no trials of the practicality of the system were carried out.
However, Allied intelligence came to know of these projects, and the US Navy developed a counter-measure, known as Operation Teardrop. This operation was carried out in early 1945 when a group of U-boats were detected heading for the US east coast. Most of these submarines were quickly pounced on in Mid-Atlantic and destroyed in the massive anti-submarine operation, though post-war analysis showed no credible missile threat had existed.