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Trial-S-Boats and Small-S-Boats developed by the K-Unit od the KM


Developments of the KM

Towards the end of the war great efforts were made, to build Small-S-Boats besides of the Light-S-Boats "LS".  

LS-Boat during Sea-Trials - Picture: Archives Förderverein 


Already 1932 to 1935 the German Dr. Tietjens worked on hydrofoils in America. 1932 he brought a hydrofoil of 6 m length and 240 kg weight on Delaware river in America to 22 kts with the help of a 5 PS-motor. After his return to Germany he reached a speed of 25 kts with a 5,5 m boat with 370 kg weight with two persons and 28 kts with one person on board by a propulsion of a 10-PS gasoline-engine. In his constructions there was a  curved or a V-shaped main hydrofoil in the center under the boat and in the middle of the rear end a hydrofoil took over the role of a supporting plane and of an elevator.

From 1927 on Baron von Schertel worked on hydrofoils. His Hydrofoil-system consisted of normally two V-shaped hydrofoils forward and aft. 1936 Schertel achieved with his eights boat built the awaited result. The boat driven by a 50 PS gasoline-engine made during tests on river Rhine with five Person on board a speed of 29 kts.

From 1937 on Baron von Schertel co-operated with the Gebrüder Sachsenberg AG at Rosslau. Already 1938 from this co-operation originated the first Schertel-Sachsenberg hydrofoil. The boat built at Wiesbaden at a length of 9,5 m an a weight of 2,8 t was propelled by a 150-PS gasoline-engine and reached a speed of 40 kts. The boat was in operation until 1945.

In summer 1939 the Sachsenberg-Shipyard got the order to build a 100-t-aluminium-hydrofoil in accordance with the System Schertel. At the outbreak of the war however the order was cancelled.

„TS 1“ to „TS 6“

In summer 1940 the Sachsenberg-Shipyard got the order for 36 small hydrofoils with a displacement of 3,8 ts, which were to be used in the surveillance of the Norwegian Fjords.  The order was later reduced to six boats. The boats „TS 1“ to „TS 5“ became because of the building of steel as V-shaped gliders somewhat heavier than thought and displaced 4,9 ts empty respectively 6,3 ts full load. The length was 11,96 m and the beam 2,7 m. The draft was 1,7 m, airborne 0,85 m. The propulsion was performed by a  380-PS Lorrain-Dietrich gasoline-engine, which brought the boat to a speed of 40 kts. The boat was armed with a 15-mm-Air Force-MG in a turn-ring-carriage with an acrylic glass-dome and manned by four men. The boat „TS 6“ was not completed before the end of the war, since it had to be reconstructed by order of the OKM. Instead of the very long propeller-shaft, in which reverberations occurred, a cone-wheel-Z-transmission should be used. The boat captured by the Russians was completed under their control, tested and transferred to the Wolga river.


Hydrofoil "TS 1" at full speed - Picture from Fock Schnellboote Vol. 2


„VS 5“

All following hydrofoils got the designation trial-S-boats (Versuchs-Schnellboote = „VS“). „VS 1“ to „VS 4“ were plans not realized. „VS 5“ was a floodable „Half-Submarine-S-Boat“. It was expected to reach a speed of 50 kts by a propulsion of four 1500/2050-PS-MAN-11-cylinder-fourstroke-diesels L 11 working on one propeller shaft. As armament two 20-mm-machineguns and two 53,3-cm-torpedo-tubes were planned. Already the first trials proved, that the boat was a total bad design.


Half-submersible "VS 5"- Picture from Fock Schnellboote Vol. 2

„VS 6“

End of 1940 the Sachsenberg-Shipyard got the order to build a trial-hydrofoil-S-Boat „VS 6“. It was to be a fast minelayer with a loading capacity for four  TMB-mines, armed with a 20-mm-machinegun on a turn-ring-carriage with an acrylic glass-dome. The complement was to consist of four men. The boat had a length of 15,74 m, beam of the hull 4,25 m, beam across the foils 5,27 m, draft 2,3 m, airborne 0,96 m. Propelled by two 700-PS-Avia-V 36 gasoline-engines working on two propeller-shafts the boat was expected to develop a speed of 47 kts. The range at full speed was to be 300 nm. During the sea trials it was detected that the steel of the hull was too week. With an accordingly strengthened plating of the boat which was more slim in the forward part of the hull the boat served until the end of the war as a test-platform for trials with different foils. It became British war loot.


Hydrofoil "VS 6" at seatrials - Picture from Fock Schnellboote Vol. 2


„VS 7“

To be able to draw comparisons between the Schertel and the Tietjens hydrofoils, Professor Tietjens got the order to build a boat with the same dimensions as „VS 6“. The boat was built as a steel-boat with bent ribs and had a construction-displacement of 17 ts but was also 4,5 ts heavier than planned. The propulsion was planned to utilize 675-PS-Avia gasoline-engines.  Since the hull was not able to made lighter, the Vertens-Shipyard at Schleswig got the order in 1942 to build a new boat with identical propulsion and the same designator „VS 7“. The boat had the dimensions length 14,00, beam 3,95 m and was built from special  tapofilm-glued poplar-playwood of a strength of 14 mm up front and 12 mm astern, It was armed with a 20-mm-machinegun on a  turn-ring-carriage with an acrylic glass-dome and two 45-cm-stern-torpedotubes. Thereby it displaced 15 ts fully loaded. Propelled was the craft by two 675-PS-Avia-Otto-motors and reached a speed of 54,5 kts. The complement was four men. The boat was completed in fall 1942 and was merely operated for trials in the Baltic.  

"VS 7" at trials in the Baltic - Picture from Fock Schnellboote Vol. 2   

„VS 8“ – „VS 9“

In fall 1942 the Sachsenberg-Shipyard got the order to build two big test-hydrofoil-S-boats. They got the designators „VS 8“ and „VS 9“. The boats were thought as transport-vehicles for one tank of 26 ts for supply of the Africa-Corps with corresponding defence against fighter-bombers and high speed. The boat was built at Harburg as an aluminium bent-ribs glider with a plane. At a length of 31,9 m, a beam of the hull of 8,0 m (across the foils 10,62 m) and a draft of 4,25 m (airborne 2,0 m) it had a displacement of 70 ts empty with a loading capacity of 28 ts. The propulsion was performed by two 2500-PS-Daimler-Benz 20-cylinder diesels MB 511 working on two propeller shafts. It was to reach a speed of 41 kts at constant speed and  45 kts at short-time maximal speed. The armament consisted of 15-mm-Air Force-MGs in turn-ring-carriages with acrylic glass-domes. The complement was 22 men.  

Hydrofoil "VS 8" at Sachsenber-Shipyard- Picture from Fock Schnellboote Vol. 2

The trails resulted in that the boat was 5 ts heavier than planned and that it reached a speed of 41 kts, since the two planned motors had been substituted by two 2000-PS MB 501 diesels, with that the boat could maintain a speed of 37 kts against the sea at a height of the waves of  1,8 m and that in spite of the sea-water-resistant aluminium in the area of the forward end of the boat strong effects of corrosion by the spray were observed

In September 1944 „VS 8“ run aground in a tempest off Hela and had to be given up.

 „VS 9“ was to get a cone-wheel-Z-transmission instead of the long shafts. That, however, remained an incomplete planning.


"VS 8" during high-speed trials in the Baltic - Picture from Fock Schnellboote Vol. 2

„VS 10“

The OKM in 1942 ordered Sachsenberg-Shipyard to build a hydrofoil-S-Boat with the designation „VS 10“. At a length of 23,3 m, a beam of the hull 6,4 m (across hydrofoils 8,0 m) and a draft of 3,3 m (airborne 1,3 m) had a displacement of 46 ts, the propulsion was to consist of four 1500-PS-Isotta-Fraschini-ASM-185 gasoline-engines and with two propellers reached a speed of 58 kts and achieved a range of 300 nm at a speed of 58 kts. The armament was to consist of six 15-mm-Liftwaffen-machineguns on turn-ring-carriages with acrylic glass-domes and two 45-cm respectively 53,3-cm-torpedotubes. The complement was to be 22 men. The boat was destroyed at the shipyard by an Allied bomb raid a few days before the planned the trials.  


German Hydrofoil "VS 10" during shipyard-trials - Picture: Archives R. Nordland

 None of the hydrofoil-S-boats developed and built with great efforts came at any time to a service at the front.    


The conventional Small-S-Boats

Type SMA

From May 1944 on in Germany the Italian Small-S-Boat Motoscafo Turismo Silurante Modificato Allargato (M.T.S.M.A. or briefly SMA) was bought in Italy respectively copied. The boat had a length of 8,8 m, a beam of 2,32 m and a draft of 0,7 m. At a displacement of 3,71 ts a propulsion-plant of two 95-PS Alfa-Romeo-A.R.-6c-2500 gasoline-engines and an armament of one 45-cm-stern-torpedo-tube and two 70 kg pursuer-defence depth-charges were installed. The speed reached was 29 kts at a range of 250 nm. Of this type in total 78 boats were built in Germany from May 1944 until January 1945.

German Small-S-Boat of the Italian Type SMA – Picture from Fock Schnellboote Vol. 2


Type „Hydra“

The Small-S-Boat type „Hydra“ was a design for the Luftwaffe in a common effort of the OKM and the Kröger-Shipyard at Warnemünde. The design based upon a type of boat, that had been planned for the Luftwaffe to transport paragliders but than was put back. On 25.08.1944 the building order for two prototypes was placed. The „H 1“ and „H 2“ had a displacement of 7,45 ts with a length of 13,21 m, a beam of 3,1 m and a draft of 1,05 m. They received an Avai-Hispano-Suiza gasoline-engine 12 y 31 reduced to 650 PS. With that a speed of 36 kts was reached. There was no turn gear but only speed ahead and idling. The range was 290 nm at 25 kts, at 36 kts it was 152 nm. The armament consisted of two 45-cm-stern-torpedotubes for the aircraft-torpedo F 5 b. No information is available about actions of these boats.

Small-S-Boat „Hydra“ during seatrials – Picture from Fock Schnellboote Vol. 2

With boat „H 53“ trials were performed with a Jumo-Otto-motor. The speed reached was only 34 kts. Therefore the trials were given up. On 04.12.1944 a series of 50 boats were ordered. Another order for a series of 115 boats were placed on 08.02.1945. The shipbuilders were distributed over all Northern Germany. The boats of these series were to get a anti-aircraft-MG for self-protection. The fuel-storage was enlarged to 1400 litres in order to widen the range.  During the building process three wagons with Rolls-Royce-Merlin-motors were delivered, which did not make it to be installed, as well as only 39 boats were completed until the end of the war. About actions of these boats no information ist available.

Stuck in the planning was the idea of Ingenieur Driesen to join two „Hydra-hulls“ by struts and to arm this catamaran with four torpedo-tubes and to bring the boat with help of a jet of Messerschmidt-turbin fighter to a speed of 60 kts.


Type „Kobra“

The type „Kobra“ was a design of Ober-Ingenieur H. Docter, which was made on the basis of an invitation of tenders. The boat was to be used as an autonomous Small-S-Boat or as a boat to be operated from a bigger ship as a bearer. It had the dimensions length 8,72 m, beam 2,5 m and draft 0,56 m. It displaced 3,46 ts and was armed with a 45-cm-stern-torpedo-tube for the torpedo F 5 b and was to be propelled by two 90 PS Ford-8-cyllinder gasoline-engines with two shafts and two propellers to a speed of 29 kts.

Small-S-.Boat Type „Kobra“ – Picture from Fock Schnellboote Vol. 2

At the end of comparing tests with other Small-S-Boats the type „Kobra“ was no longer pursued.

A design for a Small-S-.Boat of 10,6 m length, 3,2 m beam and a draft of 0,55 m was planned for two launching gears on either side for the 45-cm-aircraft-torpedo F 5b. The boat displöacing 7,65 ts was to get a propulsion with two  Hispano-Suiza gasoline-engines 12 y 31 and reach about 37 kts. The design was not pursued to an end.


Typ „KS“

The S-Boats developed by Lürssen-Shipyard in co-operation with Ministerialrat Dyckmann with dimensions of 15,95 m length, 3,5 m beam and a draft of 1,1 m were in the first place utilized as Coastal Minelayers (Küstenminenleger = „KM“). The propulsion of these boats displacing 19 ts existed of two not reversible 550/650 PS BMW 12-cyllinder-fourstroke-gaoline-aircraft-engines, which gave the boats speeds of 30 to 32 kts empty and 24 kts fully loaded. The boats got two 15-mm-Luftwaffen-MGs.

Coastal Minenlayer Type „KM 1“ - Picture from Fock Schnellboote Vol. 2

The first boats were finished 1942. Four boats were shipped to the Gulf of Finland also were boats shipped to the Black Sea. Early 1944 eight boats were originally subordinated to the Danube-Flotilla but than in the middle of 1944 they were given to Croatia. There they were designated “KS 1“ to „KS 8“. „KS 8“ burned out, „KS 5“ deserted to the partisans. The other boats were taken back by the Kriegsmarine.

From summer 1944 a part of the KM-Boats were fitted with  two 45-cm-aluminium-torpedo-tubes and a 2-cm-machinegun and designated as Coastal-S-Boats („Küstenschnellboote“ = „KS“-Boats). The „KS-Boats“ had the numbers 1, 2, 9, 10, 11, 12, 16, 17, 18, 20, 21, 23, 24, 25, 26, 31, 32, 33, 34, 35, and 36. The fate und the whereabouts oft he boats is not comprehensible.

Small S-Boat Type „KS 1“ – Picture from Fock Schnellboote Vol. 2

Devlopment of the K-Units

Within the Small-Fighting-Craft Unit (Kleinkampfmittel-Verband = K-Verband) noteworthy Small-S-Boats were developed. The leader of the Construction and Test Department of the unit, Oblt.z.S. d.R. Fr. H. Wendel, conducted on a provisional test-site at Boizenburg at the river Elbe model-towing-tests to get answers for the fundamental question whether conventional or totally new shapes should be used as hulls. Exact measurements could not be gained on this provisional test-site but a comparative evaluation was possible. As well gliders without step as gliders with step, catamaran-gliders and a boat sailing on four gliding-planes following an idea of Prof. Wankel were tested.


Type „Schlitten I“

In expectation oft he Allied invasion in northern France frameless Small-S-Boats were built at Borgward-Fyctories at Bremen in sheet-steel-shell construction. The craft was conceived as a one-man-boat easy to build with help of bodywork-presses and in high numbers. It had a length of 7,50 m, a beam of 1,60 m and a draft of 0,55 m.

„Schlitten I“ being launched from a bigger ship – Picture from Fock Schnellboote Vol. 2

Two standard-torpedoes G 7 a respectively G 7 e could be carried in two spaces in the hull. A  90 PS gasoline-engine was utilized for propulsion. With it the prototype reached 12 kts in trials with torpedoes loaded but only using the own propulsion. For the attack, the torpedoes could be started and used for the propulsion of the boat. With that a speed of 25 kts could be achieved. The boat without torpedoes could proceed at 18 kts. The range was 300 nm at marching-speed.

„Schlitten I“, G 7 a in the side-openings, in the middle propeller and rudder – Picture from Fock Schnellboote Vol. 2

The positive experiences made with this type during the trails considering the small dimensions and the weakness of the propulsion lead to the planning of a bigger and more seaworthy boat with a stronger propulsion-system with the same construction features as in „Schlitten I“.

Small-S-Boat Typ „Schlitten I“ at full speed – Picture from Fock Schnellboote Vol. 2


Type „Schlitten II“

Developed further from „Schlitten I“ the boat „Schlitten II“ had a length of 8,5 m, a beam of 1,70 m and a draft of 0,55 m. The boat obtained a 600 PS gasoline-aircraft-engine and reached thereby with torpedoes 20 kts sustained speed. The maximum speed with torpedoes was 30 kts and after launching of the torpedoes the boat could retreat at 48 kts. A MG 34 respectively MG 44 was used for self-protection. The range was 300 nm.

„Schlitten II“ on the especially developed trailer – Picture from Fock Schnellboote Vol. 2

The crew was a helmsman and an engineer from the Luftwaffe, since the Navy did not train men for this high-performance engine.

During the trials it showed, that the boat listed considerably by effect of the propeller and only at higher speed the effect of the water-stream on the bottom of the boat compensated for that.


Type „Wal I“

Early August 1944 the K-Unit developed a 9-m-plane-boat. This boat got the name “Wal I” (Whale). The hull consisted of fully-welded steel and had a length of 9,0 m, a beam of 2,3 m and a draft of 0,40 m without propeller. The boat displacing 4,2 ts got a 700 PS gasoline-aircraft-engine, which gave the boat a speed of 39 kts with torpedoes and 42 kts without. The range was 300 nm. Since the conventional torpedo-tubes were to heavy for the boat, a special construction was made to fire the torpedoes with a powder-catridge.

Small-S-Boat Type „Wal I“ – Picture from Fock Schnellboote Vol. 2

As armament served two 45-cm stern-torpedo-tubes for the aircraft-torpedo F 5 b, one 13-mm-MG and two 86-mm-rocket launchers. The crew were a helmsman and an engineer from the Luftwaffe.


Type „Wal II“

Since the OKM objected to the type „Wal I“ as plane-glider because of limited seaworthyness and possible strength and tightness problems the plane-less „Wal II“ was developed. It had a length of 10,00 m. The boat was built at Boizenburg. The 700-PS gasoline-aircraft-engine brought the boat to 38 kts with two tropedoes and to 42 kts without. The armament consisted as in “Wal I” of two 45-cm stern-torpedo-tubes, one 13-mm MG 34 resp. MG 44, and two 86-mm rocket-launchers. The rocket-launcher could launch explosive, fragment, parachute, and fog ammunition.

The boat could be launched directly from its trailer driven into the water.


Small-S-Boat Type „Wal II“  – Picture from Fock Schnellboote Vol. 2


Type „Wal III“

Because of the limited availability of steel the type „Wal“ was redesigned again. „Wal III“ emerged, which was built as a conventional wood-construction. All experiences made with the predecessor-types were taken into account. The crew was increased to three to four men in order to allow for relief during the march back and forth. As propulsion-plant alternatively 600-PS or 800-PS gasoline-aircraft-engines were planned.  Thereby the boat reached a speed of 35 resp. 39 kts with torpedoes and 38 resp. 42 kts without.

 In type „Wal III“ rockets to assist take-off obtained from the Luftwaffe were tested to provide the boats with a higher escape speed after having launched their torpedoes. The speed could be increased to 58 kts and the exhaust fumes had an effect like a red-brown fog-wall. The trials resulted in the experience that the boat could not be kept on course well and that it could even capsize. Therefore, this trails were called off. The series-building of „Wal III“ did not happen because the OKM hade made up their mind fort he type „Hydra“ as a result oft he comparative testing.


Projects of the K-Unit

A large number of plans and of the K-Unit among others also the most different hydrofoils were not pursued because of the development of the war and were only pursued after the war.