The Type XXI U-boat

The Type XXI U-boat was one of the few types of weapon that, despite being unable to take part in combat, completely changed the character of naval actions at sea.

It was the first true submarine in history. The other types of vessels designed so far were basically “diving ships” that might have been underwater for some time, but most of the time they had to be on the surface because their underwater range was severely limited. Under water they were slow and not manoeuvrable, and often had to emerge onto the surface to charge their electric batteries. The Type XXI was designed from the outset as a true submarine whose natural environment was to be the deep seas.
Unfortunately, due to various reasons, it did not have the expected impact on the course of  maritime activities during the Second World War, despite the expenditure by the Third Reich of enormous material and energy resources on this ingenious project. Eventually, only three submarines of the XXI Type managed to perform combat patrols by the end of the war.

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The concept is born
The origins of the Type XXI began at the end of 1942, when it became clear that the Allies were getting better and better at fighting German submarines, and in that situation the existing “workhorses” of the battles for the Atlantic – the Type VII and Type IX - were becoming outdated. Allied warships and aircraft sank more and more U-boats month by month, and the new German-made improvements in the construction of the old types and electronic warfare equipment to fight the Allies were not working to their desired extent. An excellent example of such a change in construction was the removal of 88 mm or 105 mm onboard guns to allow more anti-aircraft weapons to be fitted. Unfortunately, apart from a few cases, it did not happen that the U-boat was suddenly able to protect itself against air attack. In addition, the greater number of AA guns on the conning tower increased the boat’s underwater resistance, thereby reducing its range and speed. Even technological innovations such as Schnorchel (“snorkel” - a special device used to draw air for diesel engines during submerged travel) and radar warning electronic devices such as Metox and Naxos had failed to restore the balance.
At that time, Professor Helmut Walter worked intensively on the design of new types of submarines with improved hydrodynamic silhouette and a new type of atmospherically-independent propulsion, which achieved an underwater speed of 26 knots (V 80 – the author). The result of this effort was the Walter turbine project of the Type XVIII submarine with a displacement of 1,652 tons and an underwater speed of 24 knots. However, in May 1943, the concept of use of the Type XVIII hull design was introduced and it was fitted with a conventional diesel-electric drive. This idea was enthusiastically welcomed, and not only because the bigger hull gave new possibilities for designing completely new technological solutions. Due to the very serious situation of the U-bootwaffe, the project was approved on 19 June by Dönitz, and the whole program of construction of the Type XXI was accepted the following day. The pace of the work was really fast, as the detailed design and production work was carried out in parallel. This resulted in the fact that on 18 December 1943, the “Section I” was ready. The first U-boat of Type XXI (U 3501 – the author) was launched at the Schichau Shipyard on 19 April 1944, and by the end of the war German shipyards managed to launch as many as 131 such submarines. Still, only two of them achieved the status of operational readiness and performed combat patrols. Looking at it from this point of view, the whole programme ended in a complete failure for the Third Reich.

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The project

Thanks to the fact that the hull of Professor Walter’s Type XVIII project was used, a lot of time was saved, because the model tank tests and hydrodynamic calculations were already done for this model. But besides these, almost all the rest had to be designed from scratch. The Type XXI had a very streamlined outer hull and was designed to minimize hydrodynamic resistance. There were no guns on the outer deck, and two 20 mm twin-barrel anti-aircraft guns were mounted in streamlined turrets perfectly suited for both ends of the conning tower. In turn, all the protruding elements on the conning tower such as Schnorchel, the radar antenna and the radio direction finder antenna were lowered and hidden inside the hull when they were not in use. The idea of ​​an open combat bridge was also abandoned. The Type XXI had three individual posts - for the watch officer and two observers (as in modern submarines – the author).
The rigid hull was made of 26 mm thick (37 mm around hatches – the author) in the ship’s central sections and 18 mm thick in the bow and stern sections made of special steel alloy (St 52 HP) and aluminium. On the cross-section, the rigid hull resembled an “8” with its upper part larger than the bottom, which greatly increased the space of interior.