Black May (1943)

German response[edit]

The Germans tried to turn the campaign in the Atlantic back in their favour by introducing tactical and technological changes. The first tactical change saw U-boats starting operations in new waters, such as the Indian Ocean, in the hope that their targets would be less defended. Although the U-boats found fewer escort ships, there were also fewer merchant ships to sink. The far-away U-boats were called the Monsun Gruppe.


Another tactical change was to try to counter Allied air power by fighting on the surface rather than diving. When U-333 came under attack from an aircraft in March 1943, rather than diving, she stayed on the surface and shot down the attacking aircraft. It was hoped that this success could be repeated if U-boats were given better anti-aircraft defences.


To facilitate this several U-boats were converted to flak U-boats (such as U-441), but they proved unsuccessful. At first, the flak U-boats gave the Allies a shock but they soon welcomed attempts by U-boats to prolong their stay on the surface. Additional defences against aircraft was offset by the U-boat having to remain on the surface longer, increasing the chance of the submarine's pressure hull being punctured. The gunners' effectiveness was limited by the lack of protection from strafing aircraft, and Allied pilots often called in surface reinforcements to deal with flak U-boats. Furthermore, the extra anti-aircraft guns caused drag when the U-boat was submerged. The U-333 incident had proved to be the exception rather than the rule and the flak experiment was abandoned after six months; the best defence for U-boats against aircraft was to dive if attacked.


New technologies were also tried as a way to regain the upper hand. In mid-1943, two new technologies were introduced to the U-boats: the Wanze radar warning device and T5 Zaunkönig torpedoes. The Wanze warning device was designed to give U-boats advance warning of aircraft by detecting incoming radar waves so that the U-boats could dive before the aircraft started its attack run. The T5 Zaunkönig torpedoes were designed to zigzag in the hope that they would have a better chance of finding a target within a convoy. The Allies, in turn, introduced the Foxer noisemaking decoy in an attempt to defeat the acoustic homing device of the T5 torpedo. As a response, the Germans developed the T11 torpedo that was designed to ignore noisemaking decoys, but the war ended before it could be deployed.


The first U-boats fitted with snorkels (German: Schnorchel) went into service in August 1943. The snorkel was basically an extendable pipe that allowed U-boats to take in air without surfacing, allowing the U-boat's diesel engines to run submerged for longer periods. However, the snorkel suffered from technical problems and did not see wide use until mid-1944. Allied radar also became precise enough to pick up even the small target of the snorkel.


The UBW also developed a radically new submarine design, the Elektroboot (the Type XXI and Type XXIII boats). Elektrobootes did not need to surface at all during operations, however the first Elektrobootes were commissioned too late to see combat in the war.


None of the new tactics or technologies could turn the tide of war for the U-boat arm and heavy losses of U-boats continued. After May 1943, the rate of loss of U-boats was greater than the rate at which new U-boats were commissioned, and the number of operational U-boats slowly declined.