WUNDERWAFFE: SUBMERGED STRIKE
U-511: THE ROCKET U-BOAT
The history of the development of German rockets for combat missions in the Second World War, especially the V-1 and V-2 and their use, has been extensively researched and published in many books. These rockets, dubbed " Wunderwaffen " (miracle weapons) by popular science, were used from June 1944 onwards, mainly against England, after enormous human and material resources had been invested in their development during the first years of the war and the start of mass production under the cruellest of conditions. These were the V-1 and V-2, the "V" being an abbreviation for " Vergeltungswaffe" ("retaliation weapon") and the original designation Fi-103 ("Fi" = development of the aircraft company "Fieseler") being transferred to the later "V-1" and the "A-4" (A = " Aggregate") to the later "V-2". However, because of their 20 kilometre range, the Wehrmacht also developed other, much more accurate rockets for use against ground, air and sea targets.
The idea of using U-boats as a transport and launch platform for missiles was born in 1941 as the result of an unusual family coincidence, the key players of which were the brothers Kapitänleutnant Friedrich Steinhoff, commander of the U-511 and Dr Ernst Steinhoff, who worked under Wernher von Braun at the German rocket development centre Peenemünde on the Baltic island of Usedom as head of the department for rocket guidance systems.
Due to this family connection, the army's 30 cm Wk Spr 42 launcher was tested on the Baltic coast at Greifswalder Odde in the spring of 1942. This launcher could fire projectiles filled with explosive charges or flame oil up to a distance of 5,000 metres, used for area bombardment or to create fog for camouflage.
After the first test shots on 14 and 15 May 1942 from land, as well as on 27 and 28 May 1942 from a metal rack submerged in coastal waters, a total of 4 racks were mounted on the upper deck of U-511 behind the conning tower from 31 May to 4 June 1942. On 4 June 1942, 1 rocket-projectile was fired while the submarine was surfaced and a total of 6 rocket-projectiles were fired while submerged. At this time, U-511 had gone to 12 m apparent depth with the muzzles of the launch tubes of the launcher still about 5 m under water. The projectiles reached distances of between 3,000 and approx. 4,800 metres. The launch constituted the world’s first successful underwater launch of a rocket-propelled projectile.
Rocket firing tests from U-511 in the Baltic Sea
As the war progressed, the Kriegsmarine considered how its U-Boat armament could be made more effective in order to counter the constantly improving Allied defence weapons. Investigations were also carried out into attacking surface targets on land from U-Boats. In agreement with the OKW-Heer, the Peenemünde Army Institute proposed using the 30-cm Wk Spr 42 spin-stabilised artillery rocket developed by Waffenprüfamt 11 to engage targets on land, such as harbour facilities, oil refineries and so on, from a U-Boat
Consideration was also to be given to whether this weapon could also be used against Allied convoys in the Atlantic. In principle, the design of the Wk Spr 42 allowed it to be fired under water once minor defects had been rectified. After the proposal was presented to the 2nd Admiral of Submarines, Kpt. z. See von Friedeburg, the interest of the U-Boot Waffe [U-Boat arm] in this development was expressed and the preparatory work was started by Wa Prüf 11 and Heeresanstalt Peenemünde. U-511, a type IX-C boat under Kptltn. Steinhoff was chosen for the trial. This work was then completed on 4 June 1942, including submerged firing from U-511.
The results obtained at that time suggested that the 30-cm Wk Spr 42 could be effectively fired from a U-Boat from the at distances between 4 and 5 kilometres on area targets measuring 200 x 300 m to 300 x 500 m at periscope depth. The effort required to equip submarines with launchers for 30-cm Wk Spr 42 projectiles was minimal and required only 100-200 hours of labour to install. In order to test the basic possibility of launching the missile from water depths of 2.5 to 7 m, launch tests were initially carried out on 14 and 15 May 1942 from land and from the Greifswalder Oie harbour basin. The projectiles were individually mounted on a launching frame for 4 projectiles (standard series design).
Eight shots were fired from land. Shots 9 and 10 were then fired from a water depth of 2.5 metres at an elevation angle of about 45°. The 11th shot was then fired from a depth of 7 metres and only served to study the firing process. The launching frame was lowered from a ferry with the aid of a crane and the firing cable and the approximate firing direction were checked by divers. The firing range of 4,347 metres was also within the scattering range of the previous launches.
The continuation of the underwater firing tests took place on 27 and 28 May 1942, again near the Greifswalder Oie. This time, three launching frames were mounted on a common base frame so that it was possible to fire up to 12 shots in succession in the same direction. As in the previous tests, the frames were lowered from a ferry by crane into 7 metres of water. Initially, only 4 shots were fired on 27 May. Shots 1 - 3 went off simultaneously due to an error. The 4th shot, however, was flawless. The spread of shots 1 - 4 was low and in a radius of 200 to 250 metres.
Following this test, v. Friedeburg and the Peenemünde Army Institute agreed that the next firing trials of U-511 should take place and that they should be carried out at the Stettin U-Boat base after the practical exercises had been completed and special installations fitted, which took place between 31 May and 4 June 1942.
Four launching racks for a total of sixteen 30-cm Wk Spr 42 were mounted behind U-511’s conning tower in such a way that the firing direction of the racks mounted on the torpedo transport rails on the port side was to starboard and the firing racks mounted on the transport rails on the starboard side were aligned at 90° to the longitudinal axis of the boat to port.
The firing system was mounted in the conning tower and led through an existing watertight duct down below deck to the firing racks. A distribution box was located at each of the feed-throughs on the conning tower. In addition, the Oder shipyard in Szczecin installed pressurised water-tight double-pole sockets of the projectile launchers. The firing tests were scheduled to take place between 4 June 1942 and 12 June 1942. In addition to seven projectiles, which were planned to be fired on 28 May, a further 48 projectiles were prepared for target practice. The following firing programme was scheduled: On 4, 5 and 6 June 7 shots of 30 cm Wk. Spr 42 to test the mountings of the launcher racks, the firing device and the firing proceedures. The further 48 shots were expected on 7 June and were to receive a particularly reliable sealed ignition feed compared to the previous tests. The plan was to fire 8 shots each at elevations of 42, 44, 46, 48 and 50° and also to vary the water depth with a further 8 shots at the elevation angle with optimum firing range.
Unfortunately, the submarine U 511 was ordered to return to Kiel immediately on 4 June 1942, so that only 7 shots could be fired. Instead of the originally planned 2 shots from a surfaced boat, only 1 shot was fired. The launching frame was mounted at an elevation angle of approx. 45°. Firing from the boat had no effect on the submarine itself. This resulted in a firing range of 4,789 metres. The first shot was fired at around 7.30 pm. The impact was exactly in the intended direction on a land target on the horizon. The following shot would be fired from a submerged position. The diving depth was 12 metres, the projectile depth about 5 metres. The range of the submerged shot was 4,191 metres.
Again the firing had no repercussions on the boat. According to the submarine commander, Kapitänleutnant z. See Steinhoff, and the crew, the firing noise was similar to the sound of a torpedo being fired. After the next 5 projectiles had been fired, the submarine surfaced again. When the boat came out of the water it hung about 2° to port, so that the angle of elevation can be assumed to be between 42 and 43°. The diving depth for this firing sequence was about 14 metres, while the projectiles were about 7 metres below the surface. Shot 3 released at the same time as shot 4. A plug connection of the outboard socket had been temporarily interrupted, and as a result, the earthing of the firing line was disconnected and the inrush current inductively triggered shot 4 at the same time. Shots 3 and 4 impacted close together. Shots 5, 6 and 7 fired flawlessly, but shot 5 proved to be a dud. The firing range of these last five shots lay between 3,800 and 4,000 metres and was thus approx. 1 km below the optimum firing range achieved in the underwater firing tests. Based on the tests carried out at the time, the optimum firing range was probably between 4,800 and 5,000 metres at an elevation angle of around 48 - 50°. The underwater firing tests also showed that the range dispersion was generally not greater than plus/minus 100 m in the longitudinal direction.
The test firing of U-511 showed that
1. no backlash or tilt disturbances occurred during firing,
2. that the firing at minimum speed or at absolute standstill offered the most precise adherence to the firing direction,
3. that the boat must be accurately trimmed in the transverse direction to minimise longitudinal dispersion.
4. when the boat is moving, the Magnus Effect1 resulting from the swirling effect of the projectile in combination with the density of the water has an unfavourable effect on maintaining the firing trajectory,
5. the range of the upper angle groupings when shooting from water is only slightly less than when shooting from land.
In conclusion, Kapitänleutnant Steinhoff informed the participants that it was planned to complete the tests with a training boat. A final judgement on the tactical value and operational possibilities of the 30-cm Wk Spr 42 could only be made after the further tests had been carried out.
Already during the firing on 28 May 1942, the 2nd Admiral of U-Boats v. Friedeburg stated that the expected firing range of approx. 4 km was at the lowest limit of the firing range suitable for tactical use. This firing range would allow only a few enemy targets to be engaged, as it could be assumed that vital enemy industrial plants, harbour and military installations were located at a somewhat greater distance from the coast. Increasing the firing range by 4 - 8 km would have resulted in an extraordinary increase in tactical deployment options. However, calculations from the time show that the projectile would have had to be redesigned to achieve a firing range of around 12 km.
Pursuing such a project could have been considered promising at the time if the navy had wanted to, as it was within the realms of technical feasibility. In any case, the underwater firing tests showed that the projectiles were suitable for firing from submarines submerged at periscope depth. The maximum firing range achieved at that time was 5 km with a longitudinal dispersion of 250 m and a lateral dispersion of 450 m. The explosive effect of the 45 kg charge corresponded to the explosive effect of a 42 cm shell, but lacked the armour-piercing effect of the latter.
The firing rate would have been 1 - 2 shots per second, with a maximum number of about 30 - 32 shots, so that the submarine could have moved to safety directly after firing at the enemy installations. If the upper deck containers had been used to store the projectiles, 140 - 160 projectiles could have been carried. With a firing sequence of 30 rounds, 5 tactical targets could have been engaged during one enemy journey. The installation of the launching rack would not have required any structural changes, but only some additional equipment that would have been easy to carry and install.
It is still not known whether these tests were continued in practice. Projects in a similar form, which would have fulfilled the tactical tasks required by the Kriegsmarine, were continued in the last years of the war and some of them have become known.
In any case, U 511 sailed to Kiel after the trials were completed and set sail again under its commander, Kapitänleutnant Steinhoff. In July 1943, U 511 was transferred to Japan by Kapitänleutnant z. See von Schneewind and entered service there as Ro 500 on 16 September 1942. After the capitulation of Japan, Ro 500 ex. U 51l was handed over to the Americans in August 1945 and later broken up.
A TRAGIC END
On 11 May 1945, after the surrender of the Wehrmacht, Kapitänleutnant Friedrich Steinhoff and his crew of 59 surrendered to the USS Vance, a guided missile destroyer. On 17 May 1945, Steinhoff and his crew on U-873 arrived in the US coastal town of Portsmouth (New Hampshire).
Steinhoff and his men were initially interrogated in Portsmouth Naval Prison, but were then taken to the Boston neighbourhood of Charlestown. Here they were forced to march through the streets of Boston to the Suffolk County Charles Street Jail, where they were verbally abused and pelted with stones and rubbish by onlookers from the roadside. Their awards and other belongings were distributed among jail staff as souvenirs.
Civilian interrogator Jack Henry Alberti took over the interrogation of the prisoners, with a burly marine in charge of beating the interrogated when necessary. Steinhoff's face was swollen after the interrogations and had a cut on it. On 19 May 1945, he took his own life by cutting his wrist in his cell with a broken spectacle lens and a piece of wire from his service cap, causing him to bleed to death. He was buried at Fort Devens.
The content of the interrogations was kept secret. Friedrich Steinhoff is associated in particular with the tests on missile submarines in Peenemünde, but it has been speculated that the interrogations were about uranium transports to Japan on German submarines.
Due to Steinhoff's suicide, the US naval leadership initiated an official investigation. The report of 29 June 1945 stated that the distribution of the prisoners' property among the prison staff as souvenirs, as well as the use of beatings during interrogations, had been a significant violation of the Geneva Convention and the US Navy's guidelines for the treatment of prisoners. In addition, the civilian officer Jack Henry Alberti had far exceeded his authority as a civil servant by interrogating the prisoners using Navy personnel to apply force.
The Magnus effect is an observable phenomenon commonly associated with a spinning object moving through a fluid. A lift force acts on the spinning object. The path of the object may be deflected in a manner not present when the object is not spinning. The deflection can be explained by the difference in pressure of the fluid on opposite sides of the spinning object. The strength of the Magnus effect is dependent on the speed of rotation of the object.
All photos: BA RH-8 369