The Pocket U-boat Seehund Part I

Development, Construction, Technology

U-boat Type XXVII B/5 or Seehund (seal) was the most successful small-scale submarine designed and operated by the Kriegsmarine. In contrast to all its forerunners which, with the exception of Hecht, were mere submersibles, Seehund was a straightforward U-boat. Made operational in numbers earlier in the war it would have represented a dangerous threat to Allied shipping.

It was the design of naval architiects Fischer and Grim. The latter was a young engineer who had been actively employed for several years at the Kriegsmarine naval shipyard at Wilhelmshaven, and had taken the post of consultant for small-scale submarines with K-Amt Berlin (located in Schell Haus on the Tirpitzufer). This office, headed by Otto Grim and designated ‘k1Ue’ had been created in 1942 shortly after a proposal was put forward to build a 100-tonne ‘pocket U-boat’. It would be 25.33 metres long, 2.7 metres in the beam, have a draught of 2.34 metres and a surface speed of 9 knots. An armament of three torpedoes was envisaged. This project was not pursued but in 1943, after the attacks on Tirpitz by British midget submarines, consultancy office k1Ue was reactivated. Under great pressure the design for the two-man submarine Hecht was turned out while in parallel K-Amt worked on a series of ideas designated Type XXVIIB. These would have a long range, carry several torpedoes and have diesel-electric drive. The first blueprints, completed in June 1944, bore a strong resemblance to Hecht.

The torpedo-like hull had a bow section for better sea-keeping when surfaced, and saddle tanks. Enlarging the keel to accommodate the batteries made more space available in the boat’s interior. The two torpedoes were suspended from two grabs alongside the hull. A 22 hp diesel engine provided surface drive. Speed was designed to be 5.5 knots surfaced and 6.9 knots submerged.

The building contract for the three Seehund experimental boats U5001-U5003 was awarded to Howaldtswerke Kiel on 30 June 1944. Enthusiasm for the pocket U-boat was so great that orders and boat numbers for series production (U5001 to U6531) were allotted even before the designs had been submitted. The ministerial programme of June 1944 wanted a thousand. Schichau Werft at Elbing in East Prussia and Germania Werft Kiel would produce 45 and 25 boats respectively each month. Other centres for mass production were Simmering (Graz), Panker (Vienna), W. Schenk (Hall, Austria), CRDA Monfalcone (Trieste) and Klöckner-Humboldt-Deutz (Ulm).

The reality was different. Dönitz was not prepared to give Seehund priority over the large Type XXIII Elektro-Uboote. There were shortages of raw materials, skilled yard workers and transport bottlenecks. In the end, series production was concentrated mainly at Germania Werft and the Konrad bunker at Kiel no longer required for Type XXI and XXIII assembly. The three experimental boats were completed in September 1944 by Howaldt Werke. In the series production, Germania delivered 152 and Schichau 130 boats, the monthly basis being:

October 1944        35 boats

November             61

December              70

January 1945         35

February                 27

March                    46

A total of 285 Seehund were supplied to the K-Verband.

The Seehund displaced 14.9 tonnes. It was 11.9 metres in length and 1.7 metres in the beam. Fitted amidships was a small raised platform with ventilation mast, light-image reflective magnetic compass, periscope, hatch for crew access and side viewing ports. Later boats had a plexiglass cupola for navigation purposes pressure-resistant to 45 metres. Propulsion came from a Büssing 60 hp 6-cylinder heavy lorry diesel motor for surface drive and an AEG 25 hp electric motor for submerged travel. The diesel continued running submerged following a full speed alarm dive to 10 metres, in emergencies to 15 or 17 metres. This was possible because the diesel exhaust gases were expelled outboard through a vent at up to 2 atmospheres pressure. The critical depth was 20 metres, before which the engineer had to close the vent as rapidly as possible to prevent the external water pressure overcoming the exhaust pressure, entering the diesel and flooding it. The diesel fed on air in the boat. The crew would be deprived of breathable air if the diesel was kept running too long at depth. They could survive in air pressure of 550 millibars.

The Seehund had a range of 270 sea miles at 7 knots, if fitted with additional fuel tanks outside the hull up to 500 sea miles. Submerged, 63 sea miles was possible at 3 knots. Surfaced maximum speed was 7.7 knots, submerged 6 knots.

Seehund was the absolute zenith of contemporary pocket-submarine design worldwide. It could dive rapidly and be fully surfaced within four seconds. By six or seven seconds it could reach five metres. Great things were anticipated of it. The small hull would generally escape detection by radar, and not return an Asdic echo. When submerged at slow revolutions the electric motor would be barely audible to hydrophone gear. Even depth charges with the most violent shock waves would probably pass it by. At least, that was what the designers hoped for, but in practice the assumption varied from the reality.

The free-flooding forward compartment of Seehund contained the dive tanks. A tunnel below the pressure hull between the stern-most dive tank and forward of the diesel bunker held two 8 MAL 210 battery sets. Within the pressure hull the arrangement was very similar to Hecht. Forward of the control room bulkhead was the battery room with six racks (six 8 MAL 210 batteries each of 32 cells). The control room contained the driving position and two seats, one behind the other, for commander and engineer. The latter had the control panel in front of him and on the order of the commander fired the torpedo. When attacking the boat ran at periscope depth. The two (later three) metre long revolvable periscope of first class construction was inbuilt. Its optical spectrum allowed the commander to search the skies before surfacing.

Armament consisted of two standard G 7e torpedoes hung from a retaining rail secured by two protective arms either side of the keel. This arrangement required the boat to be lifted from the water and landed for reloads. Before the war’s end a Seehund-flotilla reportedly received the Walter-torpedo or K-Butt. On 28 November 1944 SKL reported that a Seehund travelled more than 300 sea miles during a four and a half day endurance voyage.

A further Type XXVIIB variant was the ‘small U-boat K’ designed for closed circuit circulating propulsion by naval architect Kurzak who had been appointed by OKM to investigate the possibilities at Germania Werft Kiel. A 15 hp diesel motor available in large numbers was adjudged suitable. A large 1,250-litre pressure flask in the keel supplied oxygen for the system. Seventy sea miles at 11–12 knots submerged was possible, 150 sea miles at an underwater cruising speed of 7.5 knots. After a discussion at OKM on 25 May 1944, Kurzak received a contract to develop the idea for a pocket U-boat. He chose the Daimler-Benz OM 67/4 100 hp motor. The engine (with an electric motor for slow running) would be ready-mounted on a common frame and slid into a stern box, secured with a few relatively accessible screws. Kurzak paid special attention to suppressing the resonance but found that four rubber shock absorbers in the corners of the frame sufficed. The designers hoped that this measure would be enough to eliminate the need for the slow-speed electric drive unit. The final result was a very light, simple engine.

Work on the Seehund closed circuit system was continued by naval architect Dr Fischer, head of the engineering bureau ‘Glückauf’ set up in the buildings of a girls’ school at Blankenburg in the Harz. An important colleague in this Type 127 design was engineer Kurt Arendt.

Contracts for the prototype Type 127 were awarded to Germania Werft Kiel and Schichau Elbing. By the war’s end Germania had three boats under contruction. These were to have received the Seehund conversion Büssing NAG-L06 diesel because so few Daimler-Benz motors were available. Bench tests confirmed that the Büssing diesel could be successfully substituted for circulatory drive purposes, but the war ended before the first prototype was ready.

Training of Seehund Crews

The Seehund crews trained at Lehrkommando 300, Neustadt/Holstein (Neukoppel) in a camp on the edge of the Wiksberg barracks, the home of 3 U-boat Lehrdivision. The exact date when this Lehrkommando was established is not certain but was probably at the end of June 1944. Presumably there was a forerunner, a small unit known as Versuchskommando 306 which had the job of preparing the training of Lehrkommando 300.

First chief of Lehrkommando 300 was LtzS Kiep, who had just completed training as a U-boat watchkeeping officer. His successor was Knight’s Cross holder Kptlt Hermann Rasch (13 ships of 81,679 tons sunk as commander of U-106). His last boat had been the trainer U-393. Rasch was temporary operations leader of the Seehund base at Ijmuiden until relieved by FKpt Brandi.

The technical shore staff head, Hecht and later Seehund instructor was initially a midshipman, Oberfähnrich (Ing) Hinrichsen. Once the Seehund boats arrived he yielded the post to Flotilla Engineer KKpt Ehrhardt. On 4 October 1944 Oblt (Ing) Palaschewski took over from Ehrhardt.

From July 1944 the volunteers, and a sprinkling of pressed men, arrived at Neustadt. As was usual with K-Verband Command all wore field-grey for camouflage purposes. Tactical training began with the delivery of the first Hecht on 26 July. It was evident almost from the outset that trained U-boat men were needed to handle the boats. It was through human error and inadequate mastery of the techniques that the fatal accidents referred to in Chapter Four occurred. Therefore only U-boat watchkeeping and engineer officers, midshipmen, cox-swains and senior engine room ratings who had undergone U-boat training qualified for Seehund training.

In September or October 1944 the first Seehund was brought to Neustadt. The training was typically hard and lasted eight weeks. It concluded with a Baltic navigation voyage over three days and torpedo-firing practice. For training purposes Lehrkommando 300 had available the survey ship Meteor, used as a target, and the torpedo preparation ship Frida Horn, a former Horn-Line steamer. The leader of torpedo practice was Kptlt Hagemann assisted by Oblt Stepputat shipped aboard Frida Horn. Probably the air-sea rescue ship Greif was attached temporarily as an escort to this command before being used to evacuate refugees from the East in the last month of hostilities. Six other air-sea rescue boats from Köslin, KFKs and communications vessels worked the torpedo retrieval routine and as escorts on training and practice sessions. The exercises took place in Neustadt Bay and between Pelzerhaken and Timmendorferstrand. Later, in April 1945, training was transferred to Wilhelmshaven (Graukoppel) and directed there by KKpt Ehrhardt. A Seehund flotilla was transported by train to Aalborg in Denmark on 23 September 1944 and at the end of the year moved from Neustadt to Holland.

The Seehund Flotilla and Its Men

Lehrkommando 300 at Neustadt had the following officer corps:

Chief: Kptlt Hermann Rasch

Adjutant: Oblt Gerhard Hermeking

Camp Commandant: Oblt Willi Demmler

Training Officers: Kptlt Klaus Ohling, Oblt Helmut Wieduwilt

Navigation Officer: Oblt Ernst-Ulrich Lorey

Torpedo Practice Leaders: Kptlt Karl-Heinz Hagenau, Oblt Manfred Stepputat, Oblt Reinhard Pfeifer

Torpedo Officers: Oblt Willi Sebald, Lt Friedrich Weinbrecht

Torpedo Officers: Oblt Willi Sebald, Lt Friedrich Weinbrecht

Acceptance Officer: Oberfähnrich Werner Hertlein

Medical Officer: Lt Dr Adolf Hollunder

The officers of Übungsflotille 311 were listed in Chapter Four, Hecht.

The officers of K-Flotilla 312 included:

Flotilla Chief: Oblt Jürgen Kiep

Torpedo Officer: Lt Paul Reinhold

Pilots/Engineers: Oblts Rudolf Drescher, Klaus-Gert Krüger, Karl Wagener, Hans-Hellmuth Seiffert, Wolfgang Bischoff; Lts Dietrich Meyer, Benedict von Pander, Winfried Scharge, Paul Reinhold, Harro Buttmann, Alwin Hullmann, Günther Markworth, Oberfähnrich Korbinian Penzhofer Which pilots and engineers were attached to K-Flotillas 313 and 314 can no longer be ascertained. From about February 1945 the Seehund crews were led as 5 K-Division. The following men were known to have been involved in sea-going missions:

Officers

Oblts: Alfred Dierks (Flotilla Engineer), Horst Kuppler, Palaschewski, Heinz Paulsen, Wolfgang Ross, Karl-Heinz Vennemann, Wolfgang Wurster.

Lts: Hans Werner Andersen, Wolfgang Bischoff, Wolfgang Böhme, Harro Buttmann, Wolfgang Demme, Karl von Dettmer, Rudolf Drescher, Claus-Dieter Drexel, Siegfried Eckloff, Horst Gaffron, Gernot Gühler, Walter Habel, Martin Hauschel, Klaus-Joachim Hellwig, Helmut Herrmann, Willi Hesel, Hinrichsen, Horstmann, Max Huber, Alwin Hullmann, Wolfgang Jäger, Ludwig Jahn, Friedrich-Wilhelm John, Wolfgang Kähler, Kallmorgen, Herbert Kempf, Jürgen Kiep, Harald Knobloch, Konrad, Henry Kretschmer, Alfred Küllmeyer, Karl-heinz Kunau, Giselher Lanz, Rolf Löbbermann, Günther Markworth, Dietrich Meyer, Friedrich Minetzke, Gerhard Müller, Ulrich Müller, Johann von Nefe und Obischau, Otmar Neubauer, Jürgen Niemann, Benedict von Pander, Werner Plappert, Heini Plottnick, Reinhold Polakowski, Werner Preusker, Winfried Ragnow, Gotthard Rosenlöcher, Felix Schäfer, Gerhard Schöne, Karl-Heinz Siegert, Wolfgang Spallek, Klaus Sparbrodt, Otto Stürzenberger, Hans Wachsmuth, Wagner, Hans Weber, Hans-Günther Wegner, Reimer Wilken, Willi Wolter, Götz-Godwin Ziepult.

Oberfähnriche: Friedrich Livonius, Korbinian Penzhofer, Streck.

Warrant Officers and Senior Ratings

Obersteuermann: Böcher, Fröhnert, Warnest.

Obermaschinist: Bauditz, Feine, Fröbel, Harte, Herde, Herold, Holst, Kässler, Nöbeling, Arno Schmidt, Stiller.

Maschinenobermaat: Langer, Sass.

Maschinenmaat: Baumgärtel, Hardacher, Heilhus, Heinicke, Heun, Jahnke, Köster, Leidige, Mitsche, Musch, Niehaus, Pawelcik, Pollmann, Radel, Reck, Rettinghausen, Rösch, Schauerte, Teichmüller, Vog(e)l.

Bootmaat: Köster.

Ranks unknown

Beltrami, Haldenberg, Huth, Knupe, Macy, Mayer, Schiffer, Schulz.

The Operations of the Seehund Crews

(Where known, the boat number and crew names are supplied, commander first, engineer second. The appropriate rank of each where known will be found in the preceding alphabetical listings.)

The Seehund base in Holland was at Ijmuiden, a district located at the entrance to the Noord Zee Kanal near the town of Velsen in the province of Noord-Holland. Velsen (population then 30,000) was an outlying suburb of Amsterdam. Besides being a large fishing port, it had jam factories, furnaces, steel and iron works, also cement, paper and chemical industries.

From 1940 Ijmuiden had been an S-boat base. The area seemed very promising for Seehund operations with its numerous tributaries and islands where the boats could be hidden from enemy air reconnaissance. The steadily growing importance of the port of Antwerp for the Allies meant that a huge number of shipping targets was available. The Noord Zee Kanal connected Amsterdam to the sea. It was constructed with a lock system designed to keep Amsterdam independent of the tides. Ijmuiden was at the seaward end of the system and had three locks of different sizes to accommodate all sizes of shipping traffic.

The HQ of K-Flotilla 312, the first Seehund flotilla, was located in an unheated two-storey building in the Rijkswaterstraat industrial area. An old mission house and the Velsen cemetery chapel served as the Operational Staff (later 5 K-Division) facility. The shore staff workshop was set up on the Hoogoven Pier, the crematorium and chapel made for a suitable food warehouse.

Aboard the boats neither roll-neck sweaters nor fur and leather jackets were effective against the Dutch winter. Since thick clothing hindered movement, the cold damp which filtered through the hatch and diesel air shaft made life miserable for the crews. Crew shipboard rations was concentrated fare poor in roughage and based on egg-white: pea-, lentil-and millet-soup cubes, rice with meat, dried vegetables, potato puree, dried egg powder, for sweet buns baked with cocoa, chocolate and almond nougat. Beverages were made from compressed bean coffee, Nescafé, compressed tea, some alcohol, also vitamin-C products, and naturally caffeine and cola nut extracts to aid alertness. Routine patrols could last up to four days and so a hotplate was installed for heating up rations as required.

Ashore the officers shared a house on the Kerkenweg in Driehus, the crews were later given a villa on the eatern side of the railway line to The Hague. The shore staff, about 100 men, were lodged in terraced housing near the small lock and in an hotel in the Velsenbeck Park. The Seehund were moored in the central lock alongside low-floating jetties.

A few days before Christmas 1944 some of the training staff were transferred to Wilhelmshaven (Graukoppel) and paired off to take over new boats. Operational leader of K-Flotilla 312 was Kptlt Hermann Rasch. The first six Seehund left Germany for Ijmuiden on Christmas Eve. Each day another group of six followed so that by the end of the year 24 Seehund had arrived at the Dutch base. On 29 December 1944 the flotilla was at readiness.

By order of Admiral Heye the first Seehund operation was scheduled for 1 January 1945 against Allied shipping in convoy lanes of the outer Scheldt between Ostend and the Kwinte Bank to position 3°10′E, and from the south coast of England against the Antwerp-bound traffic west of 10°50′E and south of 52°N. The boats would run parallel to the Dutch coast to the Hook of Holland, then pass through the eastern Hinder Kanal to reach their operational area off Ostend. From 1700 the Seehund feet – 18 boats – transited the small lock at Ijmuiden to embark on an operation expected to last three to five days. It was heavily overcast and rainy, the wind light, sea state Beaufort 2–3, but then the weather deteriorated rapidly, the wind increasing to storm force. Icy rain rattled down on the submarines, pitching and tossing in the rising seas. Vision became worse as the first combers swept the boats’ hulls. The catastrophe was about to begin.

Shortly after sailing, when still in sight of land the first casualty occurred when a Seehund hit a mine and blew up. U-5035 was forced to return with a leaky propellor shaft. Contrary to assurances that they would be invisible to radar, from intercepted enemy wireless traffic transmitted at Ostend and in the Scheldt it was soon evident that that was not the case.

The majority of the boats reached the operational area where they achieved a single success, Paulsen + Huth sinking the British trawler Hayburn Wyke, 324 tons, at 2225 on 2 January. On their return the boat struck a mine off Ijmuiden and both lost their lives. Also that day Andersen + Hardacher in U-5327 ran aground a mile west of Domburg on the enemy-occupied island of Walcheren. A farmer hid them but later they were captured by Dutch Resistance fighters after a brief firefight. The British seized the boat.

Hertlein + Haun had rudder damage. The destroyer HMS Cowdray discovered the submarine and fired on it from a quadruple-barrelled gun on the bow. The crew abandoned and were picked up by the British. Another Seehund, number unknown, was sunk on 2 January at 2002 by the frigate HMS Ekins north-east of Ostend.

On 4 January at about 1230 Kallmorgen + Vogel ran aground south of Katwijk while returning to base. The crew survived.

Scharge + Rösch had no luck. After a bomb exploding near the boat had caused little damage, they were forced to dive and depth-charged by two corvettes. Scharge ordered a torpedo fired at one of the pursuers. The torpedo stuck in the grabs. Later the diesel began to splutter, and the boat stranded off Scheveningen. After Scharge fired distress flares the crew was rescued by a naval flak battery on the evening of the seventh operational day.

U-5305 Penzhofer + Heinicke found no targets. On the return voyage the diesel broke down and the boat was run aground on the island of Voorne. Both swam to the mainland.

On 2 January U-5309 von Pander + Baumgärtel spent twelve hours in the vicinity of buoy NF8 being hunted by MGBs. The magnetic compass and diesels had failed after a depth charge attack. Sailing for home on battery drive only they eventually ran the boat aground off the Hook of Holland. A KFK brought them home.

A difficult time was experienced in U-5024 by Markworth + Spallek. After receiving serious damage from depth charging and bombing they were forced to run the boat aground on a sandbank off Goerre island. The two crew, who had spent a long time in the icy water, were found unconscious by a Wehrmacht patrol in a rubber dinghy.

Löbbermann + Plappert were surprised four miles north-east of Zeebrugge at 1655 on 5 January by a patrol boat, probably HMS Samarina. The crew was forced to abandon, were picked up by the British and brought to Ostend.

A terrible drama must have unfolded in one of the boats of the first wave. On 3 January the two crew were finished physically and mentally, their nerve gone. According to the commander’s account, at the request of the engineer the commander shot him dead and then fired a bullet into his own head. This wound was not fatal. The commander was later found adrift on the wreck of an MTB (how this came about, and whether the boat was British or German, is not explained) and he was taken to a military hospital. The outcome of the court-martial (the survivor of a suicide pact is guilty of murder) is unknown.

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