U-236 History
| Overview: | ||||
| U-235, U-236 and U-237 were sunk 14 May 1943 in the Germaniawerft shipyard in Kiel from a daylight bombing raid by the 8th AF. All three boats were raised and returned to service. | ||||
| U-236 was recommissioned on 29 September 1943 and served as a snorkel test and evaluation boat, then as a training and school boat. | ||||
| The boat was scuttled 5 May 1945 in the Baltic Sea west of Schleimünde after an attack by British Typhoon aircraft (184 and 245 Sqn RAF) the day before. | ||||
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| Dipl.-Ing. Harry Kerbs Bonn, 1 February 1985 | ||
| Former Chief Engineer "U-236" and | ||
| Ob. Ltn. (Ing.) Retired | ||
History of "U-236" |
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| Preface: | ||
| According to Rössler "The German U-Boots and their Shipyards", Volume 1, Page 118, the sister boats "U-236" (first commissioned on January 9, 1943 according to Volume 1, page 113) and "U-237" sank in an air raid on Kiel on May 14, 1943, lying in a hit floating dry-dock of the Krupp Germania shipyard. "U-236" was then decommissioned and the crew used for other purposes. | ||
| July to September 1943: | ||
| When I completed the Engineering Officer course of the Agru-Front in Hela, I was ordered to the Baubelehrung [Construction Familiarization] of a new boat intended for use at the Front, the U-boat "U-236" (Construction Number G. 666), at the Krupp Germania shipyard (GW). Kiel. | ||
| About 14 days later, the Marinebauaufsicht [Naval Construction Control] informed me that the boat would not be a Front boat, but a school boat. The OKM made this decision because of some minor dents in the pressure hull the boat had suffered when it capsized in the dry-dock. Since the prospect of having to sail on a school boat was tantamount to a debasement of the crew members who were judged fit for a Front boat, I tried to get the decision reviewed during the Baubelehrung. | ||
| A few weeks later, the final word from the responsible Marinebauaufsicht, Marinebaudirektor Hey, was that the OKM had confirmed the decision. Based on the better assessment options that exist today of the influence of pressure hull out-of-roundness on the strength behavior, this decision was entirely justified, as I know from limited experience. | ||
| After the boat was raised, almost all of the internals were taken off board and most of them were scrapped. Only the piping was said to have been reused after cleaning and sandblasting. A completely new U-boat "U-236" was created using only the old pressure hull. | ||
| It would not have been useful to go into the further course of events in more detail had this boat not been assigned a task, deviating from the usual training course of a Type VIIC Series boat, which was to gain importance for the German U-boat construction and not only for this. Since this largely remained overlooked in previous publications, it seems to me necessary to report on it. | ||
| The commissioning of the new "U-236" was scheduled for 7 September 1943. Because the future Kommandant had not yet been ordered to Baubelehrung, a few days before commissioning, as Senior Officer, I was given the task of presenting the crew to the Commander of the Construction Training Department at the commissioning ceremony. | ||
| After the crew had already lined up and was waiting for the Commander to appear, I was called to the phone. The Commander briefly informed me that the commissioning would be postponed because the boat would have a new type of device codenamed "snorkel" installed beforehand. | ||
| A snorkel mast developed by Deutsche Werke Kiel (DMK), which was the first used for a Type VIIC submarine, was installed on "U-236" in the course of September 1943. The crew, who were obligated to secrecy in this context, were mighty proud and gave | ||
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Click the flag to view the above page from the original German KTB |
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| the boat the unofficial name "U-Schnorchel 1". The boat's crest (I own a large version) became a black elephant's head with a raised trunk (snorkeling) in front of a light blue/yellow background. | ||
| 29 September 1943: | ||
| On the day of commissioning in the naval port of Kiel-Wik [the boat] joined the 5th U-Flotilla. Since "U-236" was to be used as a school boat, unlike boats intended for Front service, the Chief Engineer and the members of his technical division were ordered to the Agru-Front Hela for [only] about 14 days in order to receive technical diving team training, as one would say today. In our case, given the coming outfitting of the boat with a snorkeling system, such in-depth technical diving training [the normal longer diving training at Hela] would have been particularly important, as it later turned out. All the more so since only the future Kommandant, the I.W.O., an Obermaschinist, a Maschinenmaat and of course the Chief Engineer had already sailed on U-boats. | ||
| 30 September 1943 to January 1944: | ||
| Therefore, the Kommandant decided, on his own responsibility, to let me carry out a trim test on the day of deployment before a commission from the U-Boot-Abnahme-Kommandos (UAK) came on board. This decision was correct, even if it was made contrary to current regulations, as later experiences with embarked personnel of the UAK (naval construction officials and reserve officers from World War I) were to confirm. From then on, I also carried out intensive in-house training for the technical division as well as for the soldiers of the seamanship division who were also employed to operate the hydroplanes and rudders as well as the ballast tank venting in the interest of the safety of the boat and crew. This was done in order to meet the new and constantly changing training requirements as a result of the new system, especially with regard to reliable oder transmission (BÜ). Because we did not receive instructions, even if only about the designation of additional shut-off devices, from the flotilla nor from the UAK. The crew always showed understanding for the drills, which often continued beyond the official end of the working day. In doing so, they not only developed justified pride in their own boat, but also a pronounced feeling of togetherness, which made a significant contribution to successfully countering dangerous situations that would repeatedly arise. This team spirit continued to the bitter end. | ||
| The first snorkel mast was stowed on the starboard side above the upper deck and had to be erected by hand in an all-hands maneuver before leaving port. Equipped with this mast, after carrying out the usual trimming and diving tests, as well as balancing the boat and degaussing in the Kieler and Strander Bays, we began the first underwater transit to Sønderborg Denmark. After trimming the boat, the embarked technical training manager of the UAK, who had taken over the depth control supervision, ordered while we ran 2 x HF on E-motors (approx. 220 RPM): "Both diesels", after that "Switch to diesels". | ||
| The opening of the (what I call) the snorkel exhaust gas foot valve in the diesel room was probably assumed by him. The Control Room Mate opened the snorkel exhaust head valve on my oder as soon as I heard the diesels running. With the transition to diesel propulsion, the diesel room crew momentarily increased to the speed of 350 RPM that was actually specified for surface travel. This resulted in an underwater speed that had never been achieved before with the Type VII C (previously: AK with E-motors 267 rpm). This transition from E-motors to diesel went smoothly right away, mainly thanks to the independent and quick management of the | ||
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| crew, although we were neither prepared for it in terms of training, nor had this switching maneuver been announced in advance. On this day, for the first time, a Type VII C U-boat ran submerged with diesel engines, i.e. in snorkeling mode. | ||
| The switching maneuvers were repeated in both directions. However, there could be no talk of systematic testing of the new system. | ||
| This first still makeshift snorkel mast was soon replaced by a more practical snorkel mast to use, which was also stored on the upper deck, but now on the port side. Moreover, this could be erected by means of hydraulic oil. In contrast to the first snorkel mast, it was also equipped with a snorkel air head valve designed as a ring valve. On 11 October, 1943, we again went to Sønderborg for snorkel testing with this second snorkel system. On October 13th we returned to Kiel by diesel submerged cruise. At periscope depth, I received the order from the technical training manager to go briefly to depth 18 meters depth and then immediately back to periscope depth again. He wanted to test the functionality of the new head valve in this way. After the under-cutting of the periscope, I was able to see on the barometer how the pressure in the boat was continuously falling. I therefore reported: "Snorkel air head valve is closed". After returning to the periscope depth and freeing the periscope and the snorkel air valve, the pressure continued to drop until the barometer reached 150 mbar. So the snorkel air head valve hadn't opened again. From then on, I used the failure of the forward depth gauge (tube spring manometer) to estimate the under-pressure in the boat (analogous to the usual estimate of higher overpressure), namely 100 mbar per 1 meter error in depth, compared to the indication of the Papenberg depth gauge. Finally I reported "To Kmdt.: 200 mbar negative pressure! Question blowing?". The Kmdt. ordered "Blow!". However, the head of training prevented this with the words "Leave that to me". | ||
| Now events were rushing. The pressure in the boat suddenly dropped faster than before. There was a rushing sound from the bow compartment to the diesel compartment as a result of a strong draft. The eyes of the diving plane operators and control room men, bulging from their sockets, looked at me. My legs started shaking. I saw stars. Head of training and Control Room Mate were no longer at their stations. So I acted myself, cracked the main blow valve of the blowing distributor and with my last strength opened the the drain valve on the blowing distributor, so that not only the diving cells were blown, but air also got into the boat. Then I fell to my knees too. When I came to, the boat was "out". When the conning tower hatch was opened, there was an unusually strong pressure equalization. The men from the UAK disappeared onto the bridge and later disembarked without comment. | ||
| The following had happened in the diesel room: After closing the snorkel air head valve, the flanges of the exhaust gas lines, which were not designed for high back pressure of up to 1.8 atm at a depth of 18 meters, began to blow. The Diesel-Obermaschinist had Tauchretter donned. In order to suck away the exhaust gases quickly, the UAK naval construction officer in the diesel room (apparently unaware of the fact that the diesels were still sucking out from the boat) caused the diesels to engage the mechanical supercharger. This then led to the runaway drop in pressure in the boat. We reached 450 mbar negative pressure. | ||
| This diving mishap prompted the Ship Machinery Inspectorate (SMI) of the Navy to regularly publish so-called "Special Snorkeling Experiences" classified as secret from then on. In the meantime, sister boats "U-235" and "U-237" had also been equipped with snorkel installations. A copy of "Special Snorkeling Experiences No. 1" related to the above-described diving mishap, which I was able to save from destruction at the end of the war, is attached to this report. | ||
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| Following this event, it was decided to move away from the ring snorkel that caused the diving mishap and to return to the folding snorkel of improved design. The 1:2 scale model of this new collapsible snorkel had just been completed at the DWK when in November 1943 this shipyard was struck by a heavy air raid. Since one of my Obermaschinisten knew in which hall the model for the production of the prototype is based on the pattern, we searched for it in the rubble of the destroyed hall and actually found it lying undamaged under a work table. Due to a temporary layoff by the relevant department of the DWK, the GW was immediately commissioned to take over the snorkel development and production: so we brought the model to the GW. And there, in November 1943, "U-236" received the third snorkel installation. The snorkel mast was again on the port side, but recessed beneath the upper deck. It received a significantly improved hydraulic oil actuation and interlocks, similar to the form of the later series version for Typ VII C U-Boots. Its production, initially intended for retrofitting the front-line flotillas which were in great distress as a result of enemy radar, began in December 1943 after successful completion of the tests on "U-236". | ||
| Also worth mentioning is an infrared (IR) test that "U-236" had carried out in November 1943, the results of which were not only significant for the U-boats of the Kriegsmarine, but were important for all U-boats to this day. As part of the scientific efforts, which had been initiated after the end of 1942 due to the soaring U-boat losses, concerning U-boat locating methods possibly used on the enemy side, an IR locating device had also been developed. This device was set up on land at Aprenrade/DK about 2 km away from our passing course. We first made 3 runs: | ||
| 1st with the exhaust gas exit of the combined supply air/exhaust mast about 50 cm above the water, | ||
| 2nd with the exhaust gas exit at the waterline. | ||
| 3rd with the exhaust gas about 50 cm below the waterline. | ||
| After the first two runs, we were informed via a portable Underwater intercom that we were located clearly. Only the third run led to a negative localization result, whereupon the exhaust gas outlet was driven lower or positioned accordingly. | ||
| Then our boat had to lie fully submerged under water for 15 minutes (to cool down the boat surface). Then I had to blow the ballast tanks only with compressed air. The IR device did not show any location. Only after switching on the exhaust fan and opening the exhaust air hull valves did the IR device start up. | ||
| Mid January to the beginning of March 1944: | ||
| Mid January 1944 [U-236 was] transferred to Agru-Front, Hela. There diving technical combat training was completed. Then shipyard time at the Holmwerft in Danzig. Then transferred to the 24. U-Flottille, Memel, at the same time transferred from the 5. to the 24. U-Flottille. | ||
| 4 March to 30 April 1944: | ||
| "U-236" was torpedo shooting boat of the 24. U-Flottille, Memel. | ||
| 1 May to 31 January 1945: | ||
| "U-236" was school boat of the 21. U-Flottille, Pillau. At the end of January 1945, the boat was relocated from Pillau to Wesermünde as part of the evacuation of the Pillau U-base before the advancing Soviets. | ||
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| 1 February to 26 April 1945: | ||
| "U-236" belonged to the 31. U-Flottille, Wesermünde. Shipyard time with the Seebeckwerft, Wesermünde-Geestemünde for the purpose of conversion to a Front boat. | ||
| 26 April to 6 May 1945: | ||
| Transfer to Kiel for Front briefing and Front outfitting with provisions and torpedoes. "U-236" belonged to the 5. U-Flottille Kiel. | ||
| The further fate of the boat can be found in the attached report of the last Kommandanten, later Kapitän zur See Mumm, from 14 September 1963. | ||
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| [Z.W.O. = Zusätzlich W.O. =Supplemental Watch Officer] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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S p e c i a l S n o r k e l E x p e r i e n c e s |
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No. 1 |
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| Mechanical Superchargers | ||
| Hands off mechanical blowers ! | ||
| During a snorkeling cruise, the boat undercut substantially (about 17 meters). The float valve did not open when it emerged again. Since the diesel engine compartment was smoky from the previous exhaust gas back pressure, at this moment the supercharger was switched on by mistake in order to be able to run a higher back pressure and to ventilate. The result was that in a few seconds the already steadily decreasing pressure in the boat (float valve closed due to undercutting) suddenly fell quickly by about 400 mb to 600 mb before the engines could be brought to a standstill. With this low pressure in the boat, all verbal communication stopped. A few men went limp. A tolerable situation was slowly restored only by energetic measures, such as admitting compressed air into the boat through the drain of the blowing compressed air distributor, turning off the engines (the latter was delayed due to unfavorable transmission of orders due to the general condition). It was then very difficult to open the diesel air head valve to equalize the pressure, since the pressure in the boat was just over half atmospheric pressure. | ||
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| Beginning with this No. 1, "Special Snorkeling Experiences" were published continuously from November 1943 by the Ship Machinery Inspectorate "SMI". | ||
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View through the conning tower hatch of U-236 |
U-236 "Frontreif zeichen" |
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Agru-Front "Ready for War" symbol |