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Innovations of German World War Two submarine war

By Sakhal

At the outbreak of the Second World War, the U-boat could not be considered as a secret weapon; but certainly they could be considered as secret all of those devices created with the purpose of strengthening their characteristics. Without interferences of political character or the absence of manpower and materials, these inventions could have altered the course of the conflict.

The war demonstrated, already from the beginning, that the greatest technical efforts made by Germany during the prewar were aimed to achieve the predominance on the sea. Probably the first surprise for the British was on the field of magnetic mines, but since the Royal Navy had already experimented with them during the First World War, those could not be considered as a novelty even if the Allies were forced to an intense work to counteract them. On the other hand, the combat against the Graf Spee, along the River Plate, revealed that the German Navy possessed the radar; one not so perfected as the British models, but always capable of carrying out properly its purpose; besides, the possession of the radar by the Germans meant that the British could not sit on their laurels, and they would be forced to continue developing their radars to avoid being surpassed in turn. But the worst threat posed by Germany in the sea war came from the submarine, and it was logical that in this field was being effectuated the most intense research. Huge efforts were made to create an engine working with hydrogen peroxide and to have ready the famous Schnorkel which would allow the U-boat to remain submerged for long time, greatly diminishing the risk of being detected. The Schnorkel was in study in Netherlands when the Germans invaded that country in 1940, arrogating the invention for themselves and modifying it for being used in their U-boat; the device was basically a duct curved downwards in its top end, allowing the entry of air, but preventing the entry of water when the submarine was submerged, by means of a floater valve. But the Schnorkel became widely used only during the last months of the war, whereas from 1939 onwards the great problem for the U-boat was to be able to evade the localization effectuated by the Allied ships by means of new technical instruments. A German device introduced at the beginning of the conflict was the Bold or Pillenwerter, a perforated metallic box containing a chemical mixture. When this box was launched to the sea through a torpedo tube, the chemical components reacted producing a gas which created a thick curtain of bubbles that prevented sound waves from passing through. This allowed to counteract the Asdic and Sonar localizators in dotation in the Allied ships.

In any case it was certainly preferable for the German submarines to sight the enemy ship in advance and escape the hunting rather than using the Pillenwerter. Precisely for avoiding the enemy the U-boat were equipped with a strange flying machine, the Focke-Achgelis Fa 330 Bachstelze, similar to a helicopter. This one was actually a sort of rotary-wing kite which, remaining at an altitude of 100-125 meters above sea level, was towed by a cable attached to the U-boat. The observator aboard would be able to spot the enemy ships long before these could sight the U-boat or the very Bachstelze. As soon as an U-boat emerged to the surface to recharge the batteries or to navigate, the Bachstelze was released and in most cases it was able to spot an enemy convoy in navigation or even the enemy aircraft. If in turn it was sighted, the Bachstelze was immediately returned onboard and disassembled; at this point the submarine could submerge and escape. If instead it appeared an enemy aircraft before the Bachstelze could be retrieved, the pilot was able to use an emergency lever to detach the rotary wings and open a parachute; finally, to get rid of the fuselage he would just have to loose the safety belt of the seat. About 200 Bachstelze were built, which were used with success until 1944, when the Allied air superiority rendered useless their further usage.

Innovations of German World War Two submarine war

Another idea, of more ambitious nature, was to accommodate onboard the submarine a true reconnaissance aircraft, which could be quickly disassembled and assembled. This aircraft was built in the form of the Arado Ar 231, fitted with floaters and capable of being quickly disassembled and fit inside a special box two meters long. Its maximum speed was 160 kilometers/hour and its operational range was 500 kilometers. But when this aircraft was given in dotation to the U-boat, it was realized that the assembly was possible only with a perfectly quiet sea, so the commanders were inclined to not use it, also because they feared to be attacked while the crew tried to assemble or disassemble the aircraft. Hence the Ar 231 was replaced by the much more practical Bachstelze.

Innovations of German World War Two submarine war

Another invention - of offensive nature this time - was the Wasserel, which consisted of a bait simulating the turret of a submarine, mounted on a floater which was towed by a submerged submarine. The intention was to have an Allied ship believing the device - which was filled with a heavy explosive charge - to be a real submarine and ramming it, causing its explosion. There was no documentation demonstrating the sinking of any Allied ship by means of this contraption, also because the Wasserel was rarely used, for the commanders of the U-boat were very reluctant to enter combat with a load of one tonne of explosives in the vicinity of the submarine, and they did not like either the idea of towing the Wasserel when being chased by aircraft. Unnofficial reports stated that the few Wasserel put into sea were "lost in the sea due to incidence" soon after leaving the port.

Innovations of German World War Two submarine war

Perfected torpedoes

The main weapon of the U-boat was undoubtly the torpedo, but this one possessed numerous defects. Firstly, it was overly slow. A long-range torpedo spent four or five minutes to reach its target, whereas a cannon projectile could cover the same distance in four or five seconds. This meant that the enemy ship, during the travel of the torpedo, could move away easily, zigzag or change course. Another negative trait was that the torpedo, once launched, could not have its route corrected. Another defect, rather big, was that the torpedo left a trail behind it, which united to its slow speed rendered it as easily localizable. In the attempt of eliminating, at least in part, these inconveniences, the German technicians studied numerous projects, some of which had success. One of the most important ones was the construction, by Junkers, of an engine capable of propelling a torpedo at a speed of circa 40 knots (75 kilometers/hour), reducing to a half the time of travel and the chances of the enemy ship to avoid the impact by maneuvering. This one from Junkers was a notable technical success, for it also burned internally its exhaust gas, to avoid leaving a trail behind. The engine, of 4.5 liters with eight cylinders in V, developed 435 horsepower, which seemed incredible considering that the torpedo was as long as ten meters and weighed circa two tonnes. Still, the tune up of this engine required long time and, also because of another difficulties regarding manpower and lack of materials, it did not enter production.

Another system to render as more effective a torpedo was to equip it with a detector capable of directing it towards the target. The detector should be particularly sensitive to the magnetic field of the ship and the noise from the engines and propellers. Firstly, the technicians studied the magnetic field and in brief time they produced the corresponding detonator with magnetic detector, which should be able to make explosion when the torpedo passed close to the ship, without requiring a direct impact. But the procedures used by the Allies to render useless the magnetic mine had rendered useless as well the magnetic torpedo. But it seemed impossible that the ships could suppress the noise emitted by their propulsion plants, so in 1943 numerous U-boat were armed with torpedoes Falke, fitted with a directional detector denominated Zaunkoenig which would direct the torpedo towards the source of noise. The torpedo Falke, projected and built by Unterwasserwaffen-Versuchsanstalt at Gotenhafen, found an optimal success until the Royal Navy realized how it worked. The British technicians created then an antidote of incredible simplicity: they bought many units of the petrol hammer "Kangol" and fitted them with floaters to allow them be towed by the ships. The hammer produced much more noise than the propulsion plant of the ship so the torpedo directed towards it. The Germans replied by creating the Zaunkoenig II which, being able to distinguish the noise emitted by a hammer from the one emitted by the propulsion plant of a ship, would direct the torpedo towards the correct target; but the Allies introduced variations in the noise that the Kangol produced, deceiving again the German detector.

To increase the probability of hitting the enemy ships, particularly those grouped in a convoy, the Germans fitted many torpedoes with a device of "anarchic direction". The torpedo, as soon as being launched, should follow a regular route but, in any moment, the device would have made it to zigzag randomly. This way it was expected that the torpedo, not launched against a sole ship but against a convoy, should have zigzagged until finding a target on its course by pure coincidence. Another guidance device, able to preset a rect angle in the course of the torpedo, allowed the submarine to launch the torpedo from any position. But probably the best device created by the Germans in this field was the Schnee-Orgel, an ensemble of ten torpedo tubes mounted on the last model of U-boat and fixed in such way that, launching the torpedos in salvos, these would have their courses opened as a fan, covering an arc of ten degrees. Fortunately for the Allied convoys, few of these devices were built.

Innovations of German World War Two submarine war

Despite of technical innovations, pocket submarines or pilotable torpedoes manned by human operators, such as the Marder depicted here, were the most effective mean of putting a torpedo in the hull of an enemy ship.

Innovations of German World War Two submarine war

Cross-section of a pocket submarine Biber: 1) aft immersion tank 2) electric motor 3) endothermic engine 4) oxygen tank 5) snorkel 6) periscope 7) needle of reflection 8) batteries 9) fore immersion tank.

Perfected submarines

However, the most promising German secret weapon, in the field of naval warfare, was the submarine Type XXI. Projected in 1945, it contained many revolutionary ideas, including the Schnorkel, a particularly hydrodynamic hull, batteries of large capacity and power and a device for the fast recharge of torpedoes. Fitted with Schnorkel, the Type XXI was called the first true submarine contrarily to the previous ones, which were in fact only submersibles. The submarines of the Type XXI had 76.7 meters in length and 6.6 meters in beam, and displaced 1621 tonnes in surface. The very hydrodynamic hull and powerful electric motors allowed to reach a speed of up to 17.5 knots (32 kilometers/hour) under the water. Due to technical difficulties, the first submarine Type XXI, the U-2511, was put into sea only one week before the German surrender; during that brief time it demonstrated to be very effective, managing to escape from the British fighters easily. If it had entered production one year before, it could have been an important pawn for the Germans. Furthermore, the Type XXI influenced deeply the projects for submarines of the postwar. Another German invention was the turbine Walter, based in the utilization of the energy obtained from mixing water with very concentrated hydrogen peroxide. These engines were very effective and the submarines fitted with them tested in 1945 reached speeds of 25 knots (46 kilometers/hour) under the water. However, the high cost of the hydrogen peroxide made that these units costed almost one thousand times more than the normal ones.

Innovations of German World War Two submarine war

Cross-section of a submarine Type XXI. Red color: engine room; green color: crew accommodation; blue color: command area; yellow/orange color: battery rooms; lilac color: torpedo room.

Innovations of German World War Two submarine war

Cross-section of a Walter submarine: 1) immersion tanks 2) silent engine device 3) aft fuel-oil tank 4) Walter turbine room 5) Diesel engine 6) snorkel 7) periscope 8) turret 9) torpedo room and crew accommodation 10) trimming tank 11) lubricant oil tank 12) regulation tank 13) hydrogen peroxide tank 14) batteries 15) fore fuel-oil tank 16) commander's room 17) hydrophone room 18) radio room 19) maneuver room 20) side torpedo launchers.

Article updated: 2015-06-13

Categories: Submarines - Naval Warfare - World War Two - 20th Century - [General]


Website: Military History

Article submitted: 2015-06-13

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