When the German navy captured a British Welman midget submarine in November 1943, Commander Hans Bartels set about improving its crude design and delivered the prototype Biber (Beaver) in March 1944. There were just two problems with this project. Firstly, he copied the wrong submarine. Secondly, some of the improvements had unexpected, and ultimately fatal, consequences.
It is easy to understand why midget submarines appealed to the Kriegsmarine. Following ‘Black May’ in 1943, when 25% of the operational U-boats were lost in just one month, Germany was losing submarines faster than it could replace them. Midget submarines could be built quickly and cheaply, required just one operator, and were almost impossible to detect using ASDIC. In September 1943, midget submarines of the Royal Navy had crippled the battleship Tirpitz anchored in a Norwegian fjord. However, the Germans never saw the X-Craft actually used in the attack – and these had been substantially larger than the Welman with a four-man crew.
Welmans relied on battery power, restricting both speed and range, so the Germans added a 32hp engine to the Biber. Usually a diesel motor would propel a U-boat on the surface and recharge its batteries, but an Opel petrol engine was chosen as it was cheap and long-running. This proved to be its Achilles heel. Carbon-monoxide fumes from the engine poisoned the crew, but, because the symptoms were similar to those of seasickness, the men affected were not necessarily aware they were being gassed. Biber 90, on display in the Imperial War Museum, was found drifting off Dover in December 1944 with the its pilot dead at the controls.
Other improvements included the addition of a periscope, but it was forward mounted with only 40 degrees of vision, so the operator had no idea what was behind him before surfacing. Lacking compensating and trimming tanks, Bibers were almost impossible to operate at periscope depth anyway, so the torpedoes had to be launched while surfaced. These had a reduced range, to make them light enough for the tiny craft, so the pilot had to get close to his target and surface to attack it, eliminating the element of surprise.
On 30 August 1944, with just three weeks’ training, 20 Bibers set out from Fecamp in Normandy on their first patrol. They claimed a landing craft and Liberty ship, but no Allied losses were recorded, so this must have been wishful thinking. On the plus side, they all returned safely, a record that would not be repeated.
Having relocated to the Waal/Maas estuary in the Netherlands, Bibers claimed their one and only victory, sinking the cargo ship Alan A Dale on 23 December. All 65 crewmen survived.
The Biber pilots were not so fortunate. Of the 18 that sailed, only one returned; British MTBs sank four, one hit a mine, and 12 simply disappeared. This pattern continued until the end of the war. To make matters worse, there were two occasions when the Biber’s externally mounted torpedoes were accidentally fired in dock, destroying 25 submarines.
In total 324 Bibers were built, yet they sank just one Allied merchantman. They claimed the lives of many sailors, but unfortunately they were all German.