U-Boat Tests with Bombardment Rockets

A small Wurfkorper Spreng 42 rocket used by the Kriegsmarine to test the idea of underwater rocket launching during 1942.

Preparations for underwater rocket launching trials with U-511, a Type IXC submarine.

An hypothetical illustration of the projected modification of type XXI U-boat with a “Ursel” rocket launcher.

These images were taken from an allied report dated 1945, “German Underwater Rockets”, produced by the “U. S. Naval Technical Mission in Europe”. As you could see, of the twelve experimental rockets, five were fitted with the “bugbeluftung”, a device set at the rocket nose meant to create a layer between water and the rocket body. That was made with exhaust gas ( a small fraction diverted, like the present Russian “Skhval” ). According the report the latter designs were functioning well. Range and speed were enough for the purpose initially in mind, to defend the submarine from attacking ships. Mind the sketch, with installation aboard a U-boat. It was to be trained and launched automatically by the SP-anlage.

In 1941 scientists at Peenemunde conceived the idea of launching artillery rockets from the deck of a submarine. The Kriegsmarine showed immediate interest and this led to a series of experiments in 1942 involving U-511, a Type IXC boat. A Schweres Wurfgerat 41 rocket launcher carrying six 12in (30cm) Wurfkorper Spreng 42 rockets was fitted to the upper deck. Surface launches proved successful, but surprisingly the tests also worked well underwater to a depth of 50ft (15m).

Six rocket-launching rails were welded to the deck of the U-511, and waterproof cables were run from the rockets to a firing switch inside of the submarine. The only modification to the rockets was waterproofing them by sealing their nozzles with candlewax. The firing tests from a depth of some 25 feet (7.6 m) were entirely successful. About 24 rockets were launched from the U-511, and additional rounds were fired from a submerged launch frame. The slow movement of the submarine through the water had no effect on the accuracy of the rockets. The 275-pound (125-kg) projectiles had a range of five miles (8 km). The only problem encountered was an electrical ground that caused two rockets to fire simultaneously.

Although these were preliminary experiments, Generalmajor Walter Dornberger, the head of the Peenemünde missile facility, presented the findings to the Naval Weapons Department, contending that rocket-firing submarines could attack coastal targets in the United States. The Navy predictably rejected consideration of an Army-designed weapon, the rocket rails were removed from the U-511, and in July 1942 the submarine departed on her first war patrol.

The potential for a new anti-shipping weapon seemed good, but there were guidance issues and insufficient resources to push ahead with development. Nevertheless, some progress had been made by the end of the war under a Research and Development programme called Project Ursel.

Subsequently, as the Type XXI U-boat was being developed, a rocket system was developed for attacking pursuing surface ships. The key to this weapon was a very precise passive, short-range detection system (S-Analage passir) to detect propeller noise from ASW ships. The submerged U-boat would then launch a rocket at the target. The echo-sounding gear performed well during trials, but the rockets were still in an early stage of development when the war ended.

A V-2 rocket in launch position in the towed submarine barge Prüfstand XII. Note the control room and liquid oxygen storage underneath the rocket.

In 1943 Otto Lafferenz, a director of the Deutsche Arbeitsfront (German Labour Front), suggested the idea of launching V-1 flying bombs from submarines. This was also seriously considered but finally met with rejection for technical reasons. Then in late 1943, during a visit to Peenemunde, Lafferenz put the idea to Dornberger of launching A4 rockets at sea. The missiles were too big to be carried within a submarine and he came up with the idea of developing a submersible container carrying an A4 that could be towed behind a submarine. At a distance of 186 miles (300km) from the target (the A4’s normal range) the container would be moved to an upright position and the rocket launched. The idea met with considerable interest and the codenames Project Prüfstand XII (Test Stand XII), Apparatus F and Life Vest were assigned. But priority was being given to bringing the A4 into operational service with the Army and the development of a submarine-launched missile remained on hold until the autumn of 1944.

Eventually, a submersible torpedo shaped container was designed that measured 98ft (30m) in length and weighed 550 tons (499 tonnes). Access was gained by a hinged nose cap and the A4 missile was housed in the forward section. Behind this was a small control room and fuel storage tanks for the missile and extra diesel oil for the submarine. The container was fitted with water ballast tanks and power for all systems was supplied by a cable from the submarine. When the launch position had been reached, technicians would enter the container, prepare the rocket and finally return to the submarine. Following ignition, exhaust gas from the A4 would be re-directed through conduits around the missile and emerge at the container opening. Once the launch was completed, the container would be scuttled.

It was felt that undertaking launches against targets in Northern England and America would confuse the enemy about German rocket capabilities and make it possible to strike a number of previously inaccessible targets. Several Type XXI submarines would be adapted for rocket launch missions and one of these newer U-Boats could tow three containers, all trimmed for neutral buoyancy. Conversion of the submarines would be undertaken by Blohm & Voss in Hamburg and Wesser AG in Bremen. However, development of the project faltered and only one of three experimental containers had been completed in the Schichau Dockyard at Elbing by the end of the war. The biggest concern was ensuring container stability during launch while the accuracy of the missile’s flight presented a number of challenges that were never resolved. It is also worth mentioning that twelve dismantled A4 rockets were supplied to the Japanese and these were shipped from Bordeaux during August 1944 on U-195 and U-219, arriving in Djakarta in December 1944. What became of the wartime Japanese missile programme is unknown.

Rocket U-Boat Program

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U-511

Type IXC

Laid down 21 Feb, 1941 Deutsche Werft AG, Hamburg

Commissioned 8 Dec, 1941 Kptlt. Friedrich Steinhoff

Commanders 12.41 – 12.42

12.42 – 11.43 Kptlt. Friedrich Steinhoff

Kptlt. Fritz Schneewind

Career 4 patrols 8 Dec, 1941 – 31 Jul, 1942 4. Flottille (training)

1 Aug, 1942 – 1 Sep, 1943 10. Flottille (front boat)

Successes 5 ships sunk for a total of 41.373 tons

1 ship damaged for a total of 8.773 tons

Fate Sold to Japan on 16 Sept, 1943 and became the Japanese submarine RO 500. Surrendered at Maizuru in August 1945.

Scuttled in the Gulf of Maizuru by the US Navy on 30 April, 1946.

Postscript

In the Pacific near the end of the war, a U. S. submarine commander, Medal of Honor-winner Eugene B. Fluckey, experimented with launching rockets from his submarine while on the surface. At Pearl Harbor, Fluckey had an Army multi-barrel, 5- inch (127-mm) rocket launcher welded to the deck of the fleet submarine Barb (SS 220) and took on a store of unguided projectiles. she commenced her 12th and final patrol on 8 June.

This patrol was conducted along the coasts of the Sea of Okhotsk. For the first time in U.S. submarine warfare, Barb successfully employed rockets, against the towns of Shari, Hokkaido; Shikuka, Kashiho; and Shiritoru on Karafuto. She also bombarded the town of Kaihyo To with her regular armament, destroying 60 percent of the town.

Early on the morning of 22 June 1945, the Barb surfaced off the coast of the Japanese home island of Hokkaido and bombarded the town of Shari. The rockets were launched while the submarine was on the surface, at a range of 5,250 yards (4.8 km). During the next month the Barb remained in Japanese waters, attacking ships and carrying out five additional rocket bombardments, some supplemented by gunfire from the submarine’s 5-inch and 40-mm cannon.

The Barb’s rocket attacks were the product of one aggressive commander’s action, not part of a formal Navy program.

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