Genesis of the design

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. 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.

On 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.

Construction 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.

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.

The 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.

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

Type XXVII, Seehund(127) and Seehund(227) Technical comparison
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 O2
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.

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

Organized by one35th - last update on Saturday April 04, 2009