In addition to the remarkable systematic development of large torpedo boats for the German Navy in the second half of the 1920s and early 1930s, in the interwar period in Germany there were repeated attempts to develop small torpedo boats for performing a number of special operations. In 1934, on the basis of the U-Boot Typ I submarine developed during WWI, a new type of U-Boot Typ Typ III submarine emerged with a long sealed hangar mounted behind the wheelhouse. This hangar was equipped with everything necessary for the transportation of 2 small torpedo boats (TK).
Apparently, the developers planned to use these small TK in about the same way as towards the end of the second half of the 19th century, the naval sailors of a number of countries planned to use their then very small destroyers, which had extremely limited seaworthiness and cruising range. Then the destroyers were planned to be delivered as close as possible to enemy ports on larger carrier ships, to be unloaded using ship cranes. After unloading, destroyers in the dark were to penetrate into enemy ports or to external anchorages and, with the help of torpedoes on board, sink enemy ships. After completing the task, the TCs were supposed to return to the carrier ships waiting for them nearby and climb aboard. By 1938, the U-Boot Typ and small TKs as the second element of this weapon system began to acquire quite specific features, and even before the start of WWII, they were tried to be tested in a series of tests in the form that was presented to the head of the German submarine forces, Dönitz. For a number of reasons, these plans before WWII remained nothing more than plans. They decided to return to such plans again during the war. Small in size and very light TCs were to be delivered to enemy ship formations using Go 242 cargo gliders. And again, soon after the resumption of work on this topic, work was suspended. In 1944, it was decided to return to this idea again, and attempts began to build a small TK Hydra.
In 1936, the top management of the Kriegsmarine (OKM) firmly decided to begin the development and construction of small TKs that could be delivered to the site of alleged attacks by enemy ship formations using carrier ships - cruisers or auxiliary cruisers. Thus, the OKM, which did not have at its disposal a sufficient number of normal surface warships and submarines, decided to fight the enemy's shipping at a great distance from its own naval base. The first such project of a small TK was created by the shipyard (presumably Lürssen), taking into account the developments that took place during the WWI. The German boats LM served as the basis for the project. The boat was made of wood and light metals. A torpedo tube (TA) was installed in the bow of the boat. This project was rejected by the sailors due to the rather large size of the boat, which did not allow it to be quickly unloaded and taken on board the carrier ship on the high seas.
While the military's interest in this idea was declining due to unsatisfactory test results and all the efforts of the sailors were turned to the development of well-proven large torpedo boats with high performance characteristics, who worked in the design bureau that developed the TC, the ship engineer Docter was very became interested in the problem of creating small shopping malls. Docter proceeded from the necessary restrictions on displacement of 10-11 tons and length of 12-13 meters. Since 1937, he began research on the alternative form of the hull, power plant and issues related to weapons. The hull shape was chosen with a redan with a V-shaped bottom. Material - wooden structures and structures made of light alloys, already well-proven in the construction of large TKs, or it was supposed to use only riveted cladding joints made of light metals or a fully welded body made of V2A stainless steel. Docter was well acquainted with how such solutions were successfully tested abroad and implemented in practice by a number of leading companies. The use of an all-metal casing allowed for a weight reduction of about 10% (about 1 ton) compared to a mixed structure made of metal and wood. On the other hand, the disadvantages of an all-metal structure were also known, which consisted in the insufficient strength of such a design. The thin outer skin at the points of attachment to the frames over time, due to the constant impacts of the incoming water flow, did not hold firmly enough and was somewhat deformed when driving at high speeds, creating increased resistance. The more resilient wooden outer skin, with proper care, has always remained smoother and more preferable in terms of resistance to incoming water flow. In the end, it was nevertheless decided to proceed primarily from considerations of saving weight and stop at a completely metal case.
As for the choice of the power plant, for safety reasons, it was initially decided to use high-speed diesel engines already well-proven on large TCs, which were also distinguished by low fuel consumption. But the high-speed diesel engines manufactured at that time by MAN and Mercedes-Benz were quite large and heavy for small vehicles. In addition, MAN engines with vertically arranged counter-moving pistons during operation on large fuel tanks turned out to be not entirely reliable, since, due to their high height, they did not tolerate rolling well and created large loads on the engine foundation and from it on the boat hull at the place where the control system was installed. … At first, it was decided to test 2 Packard V-type carburetor engines suitable in size and power development. The weight of the power plant in the kit was 1.2 tons. In the future, it was planned to replace these engines with suitable diesels manufactured in Germany, which had not yet been finalized and tested.
Torpedo tubes 1 × 533 mm or 2 × 450 mm were planned to be installed in the bow or stern ends. From the practical experience gained by German sailors during WWI, it was desirable to position the torpedo tube or apparatus in such a way that it would be possible to fire torpedoes in the direction of the vehicle's movement. Increasing the load on the bow of large TCs was undesirable, but this problem was not insurmountable. At the same time, for a TK with a redan with a displacement of only 10-11 tons, such a solution could not be implemented in practice, since the bow of the small TK must be raised above the water surface to ensure normal movement. When considering the issue of torpedo armament, it was taken into account that torpedoes of 45 cm caliber carry a significantly lower explosive charge than torpedoes of 53, 3 cm caliber and, therefore, when it hits an enemy ship, such a torpedo will cause him less damage. But, on the other hand, due to the smaller size and weight on a small TC, it is possible to install 2 torpedo tubes for torpedoes of 45 cm caliber instead of one caliber 53.3 cm, and 2 torpedoes of 45 cm caliber significantly increase the probability of hitting a target. As a result, it was decided to opt for 2 torpedo tubes of 45 cm caliber, which were to be placed in the stern of the TC. The second question was the choice of the direction in which both torpedoes would be fired. If torpedoes are fired in the direction of the stern of the TC, then they can be fired only after the TC is completely turned from the target. The time required to complete the TK turn, and the turn itself, significantly increased the enemy's chances of detecting the TK even before launching torpedoes and opening fire on it from artillery systems, and would also increase the enemy's chances to evade fired torpedoes. As a result, this option was immediately abandoned. Also, torpedoes could be fired from torpedo tubes installed in the stern in the forward direction. In this case, the torpedoes were thrown from the torpedo tubes with the tail part back and moved in the same direction towards the target as the TK itself. TK immediately after dropping torpedoes had to turn aside, and the torpedoes would continue to move in a given course. The experience of the English company Thornycroft-CMB, which it gained when creating the TC during the WWII years, and the results of tests carried out by the German Experimental Torpedo Weapon Test Center (TVA), showed that the second option, in which torpedoes from aft torpedo tubes would be dropped by the tail end back, had a number of significant drawbacks. German torpedoes, when dropped into the water, had significant fluctuations in depth and could well hit the torpedo boat that released them, or at least under the influence of the boat's wake jet, significantly change the direction of movement and go past the target. TVA proposed installing torpedo tubes at the stern of the torpedo boat for firing torpedoes forward on both sides at an angle of 20 degrees. This option made it possible to install torpedo tubes at the stern of a torpedo boat, fire torpedoes forward and at the same time achieve good firing accuracy and relatively small fluctuations of torpedoes in depth immediately after entering the water. The designers developed covers for torpedo tubes measuring 2, 1 × 0, 5 m located at a low height above the water level. The military rejected this option as well, since there was a real danger that the torpedoes could jam in the torpedo tube when launched from the impact of waves created by the boat. or from natural excitement, and in the worst case, being jammed in a torpedo tube, they could even turn the boat over due to a sharp shift of the center of gravity to the side.
At the end of 1938, at the Naglo shipyard in Berlin, construction began on a small TC, designated LS1. The structure of the hull of this boat was a mixture of wooden elements and elements made of light alloys. At the same time, Dornier began manufacturing a second TC, designated LS2, at Lake Constance. The hull of this boat was completely made of light alloys. The choice of material for the LS2 body was not accidental. By that time, Dornier already had a lot of experience in this area, gained by it in the manufacture of flying boats. The dimensions of the boats were as follows: deck length 12.5 m, waterline length 12, 15 m, maximum width 3.46 m, width along frames 3.3 m, freeboard in front 1.45 m, in the middle of length 1, 27 m, aft 0.77 m, total depth in the middle of the hull length 1.94 m, draft 0.77 m, maximum propeller and rudder depth 0.92 m. Structural displacement 11.5 tons. Crew of 9 people.
During the development of the design of the boat, Daimler-Benz was ordered a prototype of the 12-cylinder V-shaped diesel engine MV-507, which was created on the basis of the DB-603 gasoline aircraft engine. The same diesel engine was offered by Daimler-Benz at about the same time as a promising tank engine. With a cylinder diameter of 162 mm and a piston stroke of 180 mm, the engine had a working volume of 44.5 liters, at 2200 rpm for no more than 3 hours it had to develop 850 hp. At 1950 rpm, the engine could develop 750 hp for a long time. Since Daimler-Benz was unable to deliver the MB-507 in the shortest possible time, it was decided to use 6-cylinder aircraft diesel engines with counter-moving pistons from Junkers Jumo 205, which developed power up to 700 hp, to test the boats. With these engines, the boats were expected to have a maximum cruising range of 300 miles at a speed of 30 knots.
With the beginning of WWII, it was decided to suspend all work on these small boats. Only work on engines and reduction gears was decided to continue. Later, in the second half of WWII, in Germany, in anticipation of the landing of the allies, it was again decided to return to the idea of creating small torpedo boats, which, according to the plans of the Kriegsmarine leadership, with an acute shortage of resources at the disposal of German industry, could somehow strengthen the coastal defenses and prevent allies during the landing. But that was a completely different story, which, due to lack of time and resources, also did not give positive results.
Rice. 1. Submarine Typ III, designed as a carrier for small torpedo boats.
Rice. 2, 2a. Schematic representation of a small LS-type torpedo boat.
Rice. 3. Small LS torpedo boat with open rear torpedo tubes.
Rice. 4. On the left side of the boat, the front cover of the left torpedo tube is visible, installed at an angle of 20 degrees to the longitudinal axis to ensure the possibility of launching torpedoes in the direction of movement of the boat.
Rice. 5. Small LS-type torpedo boat, manufactured by Dornier, during sea trials.
Rice. 6. Small LS 2 torpedo boat manufactured by Dornier.
Rice. 7, 8. Other small LS-type torpedo boats during sea trials.
Rice. 9. Small torpedo boats LS 5 and LS 6.
Rice. 10. Small torpedo boat LS 7.
