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.