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 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 -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 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.
Background
The British Area Bombing Directive issued on February 14, 1942, focused on undermining "the morale of the enemy civil population and in particular the industrial workers". According to British philosopher A. C. Grayling, Lübeck, with its timbered medieval buildings, was chosen because the Royal Air Force (RAF) Air Staff "were eager to experiment with a bombing technique using a high proportion of incendiaries" to help them carry out the directive. The RAF was aware of using a high proportion of incendiaries during bombing raids was effective because cities such as Coventry had been subject to such attacks by the Luftwaffe during the Blitz. New heavy bombers, improved navigation and bombing systems, and new tactics led to a devastating increase in the effectiveness of the RAF's bombing offensive on Germany, starting with the bombing of Lübeck in March 1942. A series of follow-up attacks using a similar pattern, was mounted against Rostock between April 24 and 27, 1942.
The destruction of Lübeck and Rostock came as a profound shock to the German leadership and population. Adolf Hitler was enraged and on April 14, 1942, he ordered "that the air war against England be given a more aggressive stamp. Accordingly, when targets are being selected, preference is to be given to those where attacks are likely to have the greatest possible effect on civilian life. Besides raids on ports and industry, terror attacks of a retaliatory nature [Vergeltungsangriffe] are to be carried out on towns other than London". In April and May 1942, the Luftwaffe designed the Baedeker Raids on British cities with the hope of forcing the Royal Air Force to reduce their actions. The Luftwaffe continued to target cities for their cultural value for the next two years. The Baedeker-type raids ended in 1944 as the Germans realized they were ineffective; unsustainable losses were being suffered for no material gain. January 1944 saw a switch to London as the principal target for retaliation. On January 21, the Luftwaffe mounted Operation Steinbock, an all-out attack on London using all of its available bomber force in the west. This too was largely a failure and German efforts were redirected toward the ports the Germans suspected were going to be used for the Allied invasion of Germany. Operation Steinbock was the last large-scale bombing campaign against England using conventional aircraft; thenceforth only the V-1 flying bomb and V-2 rockets – pioneering examples of cruise missiles and short-range ballistic missiles respectively – were used to strike British cities. The V-1 flying bomb – a pulsejet-powered cruise missile – and the V-2 rocket, a liquid-fueled ballistic missile, were long-range "retaliatory weapons" (German:) designed for strategic bombing, particularly terror bombing and the aerial bombing of cities, as retaliation for the Allied bombings against German cities.
In May 1942, following the relative failure of the Baedeker Raids, the development of flying bombs and rockets to target Britain accelerated. The V-1 flying bomb, which was developed by the Luftwaffe at Peenemünde Army Research Center, was the first of the so-called "Vengeance weapons" series. In July 1943, the V-1 flew and impacted within of its target. Ground-launched V-1s were propelled up a 49-m (160 ft)-long, inclined launch ramp consisting of eight modular sections long and a muzzle brake, to enable the missile to become airborne with an airflow strong enough to allow the pulse-jet engine to operate. The steam catapult accelerated the V-1 to a launch speed of , well above the minimum operational speed of . Its operational range was about 200 km (150 mi) and its maximum speed was about 640 km/h (400 mph).
The V-2 rocket, with the technical name Aggregat 4 (A-4) – the world's first long-range guided ballistic missile – was developed by Wernher von Braun."Long-range" in the context of the time. See The first successful test flight of a V-2 rocket took place on October 3, 1942; it reached an altitude of . The missile was powered by a liquid-propellant rocket engine and used a 75% ethanol/25% water mixture for fuel and liquid oxygen for oxidizer. The fuel and oxidizer pumps were driven by a steam turbine, and the steam was produced using concentrated hydrogen peroxide with sodium permanganate as a catalyst.
At launch, the V-2 rocket propelled itself for up to 65 seconds and a programmed motor held the inclination at the specified angle until engine shutdown, after which the rocket continued on a ballistic free-fall trajectory. The rocket reached a height of 80 km (50 mi) after shutting off the engine. Unlike the V-1, the V-2's speed and trajectory made it practically invulnerable to anti-aircraft guns and fighters as it dropped from an altitude of at approximately – up to three times the speed of sound at sea level. Its operational range was about 320 km (200 mi).
On May 26, 1943, Germany decided to put both the V-1 and the V-2 into production. On September 29, 1943, Albert Speer publicly promised retribution against the mass bombing of German cities using a "secret weapon". On June 24, 1944, the Propagandaministerium (Reich Propaganda Ministry) announcement of the Vergeltungswaffe 1 guided missile implied there would be another such weapon.
Development During World War II, several projects were undertaken by the German Navy at Peenemünde Army Research Center to develop submarine-launched rockets, flying bombs and missiles. These projects never reached combat readiness before the war ended and the German Navy did not use submarine-launched rockets or missiles.
Short-range rockets
According to Walter Dornberger, Ernst Steinhoff, the Director for Flight Mechanics, Ballistics, Guidance Control, and Instrumentation at Peenemünde Army Research Center, whose brother Kapitänleutnant Friedrich Steinhoff commanded the U-boat , originated the idea of launching solid-propellant rockets from a submerged submarine. Ernst Steinhoff was in charge of working on submarine launched rockets.
Tubular metal launch frames (Schwere Wurfgerät 41 (sWG 41)) carrying six 30 cm Wurfkörper 42 rockets were mounted on the submarine's upper deck with a 45° firing angle. From May 31 to June 5, 1942, under the code name "Project Ursel", a series of solid-fuel rocket launching experiments were carried out using submarine as a launching platform near the Greifswalder Oie.
Successful firings from the surface were carried out on June 4, 1942, and from up to underwater with no effect on the missiles' accuracy. 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. The development of this system ended in early 1943 because it was found to decrease the U-boats' seaworthiness.
From 1944 to 1945, the German Navy continued to develop and successfully tested various short-range rockets that could be launched from submerged submarines at depths of up to at the naval testing station operated by the Torpedoversuch Anstalt Eckernförde at Lake Toplitz near Bad Aussee, Austria. No official records on the deployment of these short-range rockets on German U-boats or their use against targets have been found.
The first recorded attack on land-based targets using sea-based rockets was carried out by the US submarine on June 22, 1944, against the Japanese town Shari. The USS Barb fired 12 5-inch rockets Mk 10 Mod 0, from offshore, using a rocket launcher Mk 51 Mod 0 installed on the deck of the submarine.
V-1 flying bombs In 1943, interest in the concept of sea-launched missiles was revived with the advent of the V-1 flying bomb; proposals were made to mount a V-1 and steam-operated launcher on a U-boat to strike targets at a much greater range than the that was possible from land-based sites. This proposal foundered because of inter-service rivalry; the V-1 was a Luftwaffe project.
In September 1944, the Allies received intelligence reports suggesting Germany's Kriegsmarine was planning to use submarine-launched V-1s to attack cities on the east coast of the United States. A modified German submarine was spotted in a southern Norwegian port "showing a pair of rails extending from conning tower to the bow and terminating at a flat, rectangular surface", apparently modified to launch V-1s. No official records on the deployment of V-1 flying bombs on German U-boats have yet been found.
V-2 rockets In Autumn 1943, Deutsche Arbeitsfront director Bodo Lafferentz proposed to Dornberger the idea of a towable, watertight container that could hold a V-2 rocket. The project of sea-beased V-2 rockets was code-named "Apparat F"' and the development of towable containers was commonly referred to by the codename Prüfstand XII from late 1944. The container was unmanned and unpowered, and was intended to be towed into range of its target by a U-boat then set up and launched from its gyro-stabilized platform. A report of the Peenemünde research center dated January 19, 1945, summarized the objectives of Prüfstand XII:
This project opens up the possibility of attacking, with the Apparat F, off enemy coasts (for example, northern England or eastern America), very distant but strategically important targets that are currently out of range. In addition, it deceives the adversary about the real range of the missile and, at additional costs, offers new strategic and political opportunities.
Important rocket scientists such as Klaus Riedel, Hans Hüter, Bernhard Tessman and Georg von Tiesenhausen were assigned to the project.