When the Nazis released their new Type XXI-class U-2511 submarine it was one of Hitlers “Wonder Weapons” that he promised the German people would win the war, and represented a genuine leap in the technology of submarines. Its engine was advanced for its time, allowing it to operate while submerged underwater, at high speed for considerable distances while most of the other submarines at that time operated mainly on the surface and would only dive for short periods either during an attack or to escape.

XXI Type Submarine

Kriegsmarine, as the German Navy was called, relied on their U-boats at the start of the war to strangle the UK with a blockade against her shipping traffic. By 1942, Germany had almost succeeded in isolating Britain from its colonies. They had hundreds of submarines surrounding the British Isles and all but cut them off from everyone.  Merchant ships were being sunk by U-boats faster than shipyards could replace them.  Their tactic was successful in the beginning. In October, their U-boats sank 56 ships solely in the passage between Greenland and Iceland.

U-2540 in wartime configuration and exhibited at the Maritime Museum in Bremerhaven. It is the only floating example of a Type XXI U-boat. (SicherlichCC BY-SA 3.0, via Wikimedia Commons/Retouched by Fotowerkstatt)

The success did not last long, as the new convoy tactics, radar, and anti-submarine patrol planes caused problems with their Type VII submarines. The allies had also broken the Enigma Code that gave them pretty god information on U-boat movements in the Atlantic. That meant that their existing submarines were vulnerable to detection and attack in huge numbers. The electric engines could not hold a charge for more than a few hours when recharged with diesel on the surface. In May of 1943, the Allied forces managed to destroy 43 of these U-boats, about 25% of Germany’s entire operational submarine forces. As Marcus Jones, an associate professor at the US Naval Academy, wrote,

No amount of willpower or doctrinal ingenuity on the basis of existing boat types could overcome the collective effects of the countermeasures the Allies employed so well by 1943.

The Germans realized that if they wanted to get ahead, they should develop a new kind of submarine that would change the tide of the water war. With that, propulsion engineer Helmuth Walter designed the Type XXI with a unique figure-eight interior. Its larger electric battery bay meant that the submarines of this type could run submerged for more than two days and raise a snorkel while still below the surface to run her diesels and recharge the batteries. The sub had two sets of electric motors, one set for ultra-quiet operations and another set for bursts of speed in an emergency allowing it to move at 17 knots plus while submerged. These were  Siemens-Schuckert GU 365/30 double-acting electric motors that provided more than 36kW of output, and two Siemens-Schuckert silent running GV232/28 electric motors with 166kW of output

Most convoy escorts at the time sailed were only going about 10 knots underway to travel long distances.  This was vastly superb to the older Type VII which could not travel faster than eight knots underwater and for only short periods.

It was also fast enough to keep up with convoys while running submerged. It could run silent for 60 hours at five knots. It could also pick up the pace, traveling for an hour and a half at a breakneck speed of 18 knots. This would allow her to approach a target unseen, fire her torpedoes and then dash away at high speed and depth before the escorts could react. It could also dive to nearly 1,000 feet in an age when the most advanced US Submarine, the Tambor Class could only dive to 400 feet and manage two days submerged at 2 knots.


The U-2511 was a Type XXI submarine, a German diesel-electric submarine specifically designed during World War II. Four of the 118 submarines of this type were combat-ready, two of which were put into active service and patrols, although none were used in actual combat.