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History of German SEEHUND Midget Submarine
Draft concept design of the Seehunde
Draft concept sketch, Typ XXVII B5 (127)
collaboration between MBR Grim (OKM-KIUe) and consultant engineer "Glückauft" in Blankenburg/Harz 
Photo courtesy from Die Seehunde - Klein U Boote

Genesis of the design

Seehund 3d On the whole, German midget submarine designs owed more to desperation rather than good naval design practice. There was, however, one German good design which was a cut above the rest of which, had it not been for the vast array of countermeasures deployed against them, might have made some impact on the course of the war. This craft was the Seehund or type 127 submarine. This was a two man craft armed with two torpedoes and capable of extended operations.

The original of the Seehund lay in the recovery of the remains of X6 and X7 from the depths of Kaafjord. Subsequently the Hauptamt Kriegschiffbau produced a design for a two-man midget submarine designated Type XXVIIA, also know as Hecht (Pike). Like the X-Craft, Hecht was designed to carry mines to be laid beneath the hulls of enemy ships, but it was substantially smaller and differed from its British counterpart in a number of significant ways. To begin with, Hecht’s designers saw no need for a dual diesel / electric motor propulsion system. It was envisaged that Hecht would operate submerged all the time and therefore was no need for a diesel engine. The power plant consisted of an 8 MAL 210 Battery based on five 17T torpedoes troughs driving a 12 hp AEG torpedoes engine. Even so Hecht’s endurance was a paltry 69mm at 4 Kts. Since the craft would have to pass through nets and other obstructions she was not originally fitted with hydroplanes or stabilizing fins. Instead adjustable weights on spindles were fitted inside the boat. This method proved completely ineffective since the weight could not be moved quickly enough in an emergency to affect the trim of the boat and hydroplanes and stabilizing fins had to be fitted subsequently. Even so, submerged control was very poor. Since Hecht would be operating dived, she was not fitted was ballast tanks, and two compensating tanks gave the craft sufficient buoyancy to lie awash on the surface.

Although Hecht was designed to carry an explosive charge, Donitz insisted that a torpedo be fitted so that attacks could be mounted on shipping in coastal waters.Seehund view 05 Hecht’s lack of buoyancy meant that only torpedoes without negative buoyancy could be used and these were of relatively short range. Accordingly Hecht was fitted for both torpedo carrying and mine. If a torpedo was carried then a further three battery troughs could be fitted. Externally Hecht resembled a British Welman. In the nose of the craft was the detachable mine. In the forward section were the battery and a gyrocompass. Hecht was the first German midget submarine to be fitted with gyrocompass, which was deemed essential for navigation if the craft were to be spending so much time submerged. Behind the battery was the control compartment with seats for the two-man crew, another new departure for the Germans.

The two men could offer each other mutual support and share the watch keeping/routine maintenance load. The crew sat in seat arranged fore and aft on the centerline with the engineer sitting forward and the commander aft. The latter was provided with a simple periscope and a Plexiglas dome for navigation purposes. Further aft was the electric motor.

Seehund view 06On 18 January 1944 Donitz discussed the new design with Hitler who expressed his approval for these new craft. On 9 March contracts were placed with Germaniawerft for the construction of a prototype, followed by another for fifty-two boats on 28 March. The fifty-three boat were built between May and August 1944: none saw active service but all were employed in the training role for Seehund crews. At the same time as the orders were being placed, numerous variations on the Hecht were under construction. The first was the Type XXVIIB that had increased range, an armament of two torpedoes and dual diesel/electric propulsion. The initial design was complete by the end of June 1944 and showed a craft which strongly resembled Hecht in many ways but which was fitted with a ship-shaped casing for better sea keeping while on the surface, and saddle tanks. More room had been created inside the craft by placing the battery troughs in the keel while the two torpedoes were slung externally in recesses in the hull. A 22 hp diesel as fitted for surface travel and it was estimated that this would provide a surface speed of 5.5 kts, while a 25 hp electric motor gave a submerged speed of 6.9 kts.

A variants of the Type XXVIIB was the Klein U-boot K which differed only in that it was powered by a close cycle engine. The proposal came from Chief Naval Construction Adviser Kurzak who was the Kriegmarine’s representative for closed-cycle propulsion at Germaniawerft. The boat was powered by a 95 hp diesel engine commonly use in the Kriegmarine’s small boats and which therefore available in quantity. The engine ran off oxygen, 1250 liters of which were stored in the boat’s keel at four times atmosphere pressure. It was anticipated that the boat would has a maximum submerged speed of 11-12 kts and a range of 70 miles at that speed. For long range travel, the boat would have a range of 150 miles at 7 kts. Kurzak presented his design at a meeting chaired by Vice-admiral Heye on 21 May 1944 and was requested to develop a close-cycle engine appropriate for such a submarine.

Close cycle installation on Seehund
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concept sketchConstruction and design

Kurzak’s proposal had a considerable influence on the final variants of the Type XXVII. This finally emerged as the Type XXVIIB5, better known as the Seehund (Seal) or Type 127. Seehund had a boat-shaped hull with a small raised platform amidships containing the air intake mast, the magnetic compass, the 10m periscope and a glass dome was built to withstand pressure down a depth of 45m. The casing contained the ballast tanks and a free-flooding compartment forward. Inside the pressure hull, the layout resembled that of the Hecht. In the forward part were four of the seven Mal 210 battery troughs, the other stowed in the keel. In the center of the craft was the control compartment with seats for two operators. The engineer handled the controls and fired the torpedoes on the word of the commander. During the attack the boat was kept at periscope depth and ‘talked’ onto the target by the commander. The fixed 10m periscope was of excellent design and incorporated lenses which allowed the commander to search the skies before surfacing – vital in view of overwhelming air superiority now possessed by the Allies. The armament of the Seehund was the standard two G7e torpedoes slung in recesses under the hull, which meant that the boat had to be removed from the water before loading weapons, a tiresome procedure at the best of times.

Seehund view 09

In the after part of the boat was the diesel and electric motor. Seehund were powered by a 60 hp Bussing diesel with a 25 hp AEG electric motor for submerged drive. This gave an endurance of 270nm on the surface at 7 Kts. If exterior fuel tanks were used, the range went up to as much as 500nm – although the crew’s efficiency throughout such a long passage would have been doubtful. Submerged endurance was 63nm at 3 Kts. These figures were rather disappointing and it was apparent that the hull form, particularly when torpedoes were carried, exerted considerable resistance.

Seehund view 10The first contract for Seehund construction was placed on 30 July 1944 . Enthusiasm for this craft was so great that most of the contracts and hull numbers had been allocated before the design was complete. The Ministerial Programmed of June 1944 envisaged a total of 1000 Type XXVII boats in service. Germaniawerft and Chichi at Elbing were to build twenty-five and forty-five boats per month respectively. Other centers involved in Seehund production were CRD at Monfalcone on the Adriatic and Klockner-Humbolt-Deutz at Ulm . Like so many other schemes in the Third Reich, reality fell far short of expectations. Donitz would not consent to the production of the Type XXVII U-boat being held up for Seehund construction, while raw material shortages, labor difficulties, transport problems and conflicting priorities in Germany’s crumbling war economy all combined to reduce Seehund production. In the event Seehund production was concentrated at the Konrad bunker under Germaniawerft in Kiel which was not longer required for Type XXI or Type XXIII production. A total of 285 units were built and allocated irregular numbers in the range U-5501 to U-6442.

  The production schedule for Seehund was as follows : September 1944, 3 units; October 1944, 35 units; November 1944, 61 units; December 1944, 70 units; January 1945, 46 units; February 1945, 27 units; March 1945, 46 units and April 1945, 8 units. While the design process was well in hand Chief Naval Construction Adviser Kurzak proposed the incorporation of a close-cycle power-plant into the design to achieve significant savings in volume and weight. The design was similar to the Klein U-boot K described earlier but of slightly larger dimensions. The engine installation, the Daimler Benz OM67/4 of 100 hp (with an electric motor for silent creep speed) was selected, and was to be mounted on a common frame which could be simply inserted into the stern section for easy access and secured by a few screws. Significantly, attention was paid to reducing engine noise as much as possible. The common frame was mounted on an elastic bedding using four rubber buffers at the edges of the frame. It was hoped that noise reduction measures would be effective that the silent creep speed electric motor could be dispensed with altogether thus making the power plant extremely simple and light. The closed cycle Seehund would have a submerged range of 69 nm at 11. Kts or 150 nm at 7.25 kts.

XXVII Close cycle Seehund Type 227
Close Cycle Seehund Type 227
Photo Courtesy from The U-Boat

Development of the closed cycle Seehund was carried out by Ingenioeurburo Gluckauf in Blankenburg and was given the designation Type 227. Contracts for prototypes were awarded to Germaniawerft in
Kiel and to Schichau at Elbing and by May 1945 a contract for three operational model (U-5188 to U-5190) had been awarded to Germeniawerft. These models would have used the standard Seehund power plant converted to closed cycle operation on the grounds the Daimler-Benz engines were not available in any quantity. Tests showed that the Bussing engine could be successfully converted by the world ended before the craft could go into production. Table below is a rough comparison between the original Type XXVII, the Seehund and the Type 227.

Type XXVII, Seehund(127) and Seehund(227) Technical comparison

  Type XXVII
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Type XXVII (127) Seehund
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Type XXVII (227) Seehund
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Data XXVII Seehund (127) Seehund (227)
Displacement 11.8 tons 14.9 tons 17 tons
Length 10.4 m 11.9 m 13.6 m
Beam 1.7 m 1.7 m 1.7 m
Propulsion 1 x 12 hp ET 1 x 60 hp D
1 x 25 hp E
1 x 100 hp D
1 x 25 hp E
Fuel capacity N.A. 0.5 tons 0.6 tons
+ 0.72 tons O
Speed (surfaced) N.A. 7.7 kts 8 kts
Speed (Dived) 6 kts 6 kts 10.3 kts
Range (surfaced) N.A. 300 nm @ 7kts 340 nm @8 kts
Range (Dived) 38 nm @ 4 kts 63 nm @ 3 kts 71 nm @ 10 kts
Torpedoes 1 2 2
Mines 1 0 0
Crew 2 2 2

Source from Midget Submarine of the Second World War - ISBN : 1-86176-042-6

Delivery Schedule of Seehund
The Ministerial Program of June 1944 planned a total of 1,000 Type XXVII midget U-boats, of which Elbing was to supply 45 and GW 25 boats per month. Initially, it was intended to manage without other production centers. When GW took over the complete Type XXIII construction, it would then cease to take part in the Seehund program, and production of these would then begin in southern Germany. At the beginning of January 1945, the delivery plan for Seehund was as shown in (table A)

When Schichau, Elbing, was no longer available, it was decided, on 30 January 1945, to accelerate the commencement of construction of Seehund at Klöckner-Humboldt-Deutz in Ulm, and at the firm of W.Schenk in Hall, using Elbing personnel, and to rise production to 50 boats per month by July 1945 as shown in (Table B)

At the same time, GW was to continue to deliver. The total program was reduced to 600 boats in the emergency program. As the Konrad shelter in Kiel was now required neither for Type XXI nor for XXIII, it could be used additionally by GW for Seehund construction.
Sequence production was carried on there from the middle of March, while production at Ulm, which was not very accessible from a transport point of view, was stopped and construction at Hall did not begin. The main difficulty that developed in the latter stages of the war, and was to affect even the Seehund program, was the bottleneck in accumulators. Thus in March 1945, instead of 60 Seehund batteries, only 40 could be provided.
The total of Seehund delivered is shown in (Table C).
3 Seehund was produced at Howaldt-Kiel, 135 at Schichau, Elbing, and the remainder at GW.

Delivery program for Seehund, January 1945 (Table A)

1945 Schichau, Elbing GW, Howaldt Kiel Southern Germany
January 55 25 -
February 55 25 3
March 55 30 5
April 55 30 10
May 55 25 20
June 55 - 30
July 55 - 35
Source from The U-boat - ISBN 0-304-36120-8

Revised Seehund construction program, 30 January 1945 - excluding GW(Table B)

1945 Ulm Hall
January - -
February 5 -
March 10 -
April 10 5
May 10 15
June 10 25
July 10 40
Source from The U-boat - ISBN 0-304-36120-8

Actual Delivery for Seehund (Table C)

Year/Month Seehund
1944 -
May -
June -
July -
August -
September 3
October 35
November 61
December 70


January 35
February 27
March 46
April 8
Source from The U-boat - ISBN 0-304-36120-8
German Submarine Builder :
Blohm+Voss : Blohm & Voss, Hamburg
Bremer Vulkan : AG Bremer Vulkan, Vegesack
Danzig : Danziger Werft, Danzig
Deschimag : Deschimag AG, Weser, Bremen
Deutsche Werft (with yard at Finkenwerder, Gotenhafen, Kiel, Reiherstieg )
Flender : Lubecker Flender Werke, Lubeck
Flensburg : Flensburger Schiffbau Gesellschaft, Flensburg
Germania : Friedrich Krupp AG, Germaniawerft
Howaldt : Howaldtwerke, Hamburg
KMW : Kriegsmarine-Werft, Wilhelmshaven
Nordsee : Nordseewerke Emden AG, Emden
Oderwerke : Stettiner Oderwerke, Stettin
Neptun : AG Neptun, Rostock
Schichau : F Schichau GmbH Werk, Danzig and Elbing
Seebeck : Deschimag Werk, Wesermunde
Stulcken : HC Stulcken Sohn, Hamburg

German U-boats construction yards

German U-Boat Construction Yards
Photo courtesy from : 
U-Boats - The Illustrated history of the raiders of the deep

Seehund view 11 The Seehund was the most sophisticated of all the midgets which went into production for the Kriegsmarine. From the Allied perspective its small size made it almost impossible for Asdic to get a return of her tiny hull while her very quiet slow speed made her almost impervious to hydrophone detection. As the Commander-in-Chief Portsmouth, Admiral Sir Charles Little, succinctly put it, ‘fortunately for us these damn things arrived too late in the war to do any damage”.

References :
A extract from the Book : Midget Submarine of the Second World War by Paul Kemp
ISBN : 1-86176-042-6 - Chatham Publishing

A extract from the book : The U-boat, The evolution and technical history of German Submarines
ISBN : 0-304-36120-8 - Cassell&Co




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