German U-Boat

This phase of the war between April 1941 to December 1941 saw German u-boats and the Royal Navy sparring relentlessly as both sides sought to gain the upper hand. The number of u-boats at sea was increasing significantly, but the allies sought to counter this gain with improved technology for anti-submarine warfare.

The first of the British advantage was the development of High Frequency Direction Finders (HD/DF or “huff duff”) for shipboard use. By triangulating the direction of a u-boat’s radio transmission, the equipment could reveal its bearing and approximate range from the operating vessel. The Germans were well aware that the Allies had land-based DF capability and tried to avoid falling victim to it – but they were not aware that the allies had developed one for shipboard use, neither were they aware that they could take an accurate bearing on transmissions lasting 20 seconds or less. When the location of a u-boat had been DFed, escorts would be sent to intercept it and prevent it from attacking. These u-boats were usually the shadower, whose job was to maintain contact and report the location of convoy sightings. Even if the escorts were not able to sink the u-boat, it would force it to submerge and lose contact with the convoy, and therefore prevent packs from forming against it. U-boat commanders were directed to refrain from transmitting radio messages unless absolutely necessary, but this led to new problems. First BdU was starved for information, and second, the lack of any radio message was misconstrued to mean that the u-boat was carrying out orders as assigned, rather than that the boat had been sunk.

The second major allied development was the Anti-Surface Vessel radar (ASV) for land-based aircraft. Introduced in early 1941, u-boat commanders quickly became aware that the appearance of enemy aircraft was too often for it to be due to visual sighting and correctly concluded that radar was to blame. Afterall the Luftwaffe Focke Wulf Condor had used radar effectively to locate allied convoys. This new threat forced u-boats to dive more and travel submerged to and from their patrol zones, which effectively reduced their presence on the Atlantic. Convoy escorts were also now equipped with improved ASV radars – night attacks were much more difficult to approach as u-boat’s were no longer invisible to convoy escorts. As a result, the Germans developed radar warning receivers (Metox) which alerted u-boats when they were illuminated by enemy radar. The benefits of these receivers were somewhat questionable as they not only detected enemy radar, but also transmitted a frequency which could be detected for miles around. The Germans thought the Allies were homing in on these frequencies and the confusion led to considerable problems for the Germans.

Finally, the most important development came on 9th May 1941, when the ENIGMA coding/decoding machine was captured together with the keys and other top secret papers aboard U-110 (Lemp). During a series of well conducted depth charge attacks, HMS Aubretia, Bulldog and Broadway seriously damaged U-110, cracking the hull and internal batteries. Mixed with sea water leaking into the boat, it emitted a poisonous chlorine gas which forced the boat to the surface. HMS Bulldog bore down, intending to ram the crippled boat, but reduced speed upon seeing the crew abandon ship. The captain sent a boarding party to capture the u-boat. Lemp on seeing this attempted to re-board and scuttle it, but was killed in the attempt. U-110 sank two days later while on tow, but nevertheless the damage had already been done. Several other German weather and supply vessels were also captured with top secret documents seized.

This information provided British Naval intelligence with what it needed to crack the German cryptology system. Soon German radio traffic was open to the British, providing a vast amount of information. This was of decisive importance as it provided a clear picture of u-boat locations, allowing the Royal Navy to intercept u-boats and re-route convoys. Tonnage losses began to drop as sightings became rarer.

One of the earliest German suspicions that the British were reading the Enigma codes came on the night of September 27 1941. Three u-boats were ordered to rendezvous at a remote Tarafal Bay, San Antao Island, in the Portugese Cape Verde Islands. This message was duly intercepted and the British decided to attack. In the ensuing melee, all three u-boats got away, but Donitz did not believe that the encounter had been by chance and was convinced that the British were reading the Enigma. As a result, he ordered for the Enigma keys to be changed followed by an investigation by Vice Admiral Maertens, Chief of Naval Communications. Maertens rebuked the claim and concluded that the Enigma could not be broken and the blame was probably caused by espionage – a convenient scapegoat in these circumstances.

Meanwhile, several other significant battles were fought during this time - the first of which was the legendary order by Winston Churchill to “Sink the Bismarck”. Learning that Bismarck was being hunted by the Royal Navy, Donitz deployed all available u-boats to assist Bismarck. Information from intelligence reports enabled Donitz to plot a probable track of Bismarck and her pursuers. He formed several intercepting traps in the most likely point of action, but many u-boats were either too far off or those that were in range had ran out of torpedoes. Wohlfarth in U-556 was one of them. In the Bay of Biscay, May 26, British Force H was within torpedo range of U-556. Sailing in front of him was HMS Ark Royal and HMS Renown. In frustration he logged “If only I had torpedoes now! I should not even have to approach, as I am in exactly the right position for firing. No destroyers and no zigzagging. I could get between them and finish them both. The carrier has torpedo bombers on board. I might have been able to help Bismarck.”. Several other u-boats converged and managed to witness the gun flashes and bursts of explosions, but were totally helpless in the ordeal. By May 27 10.40am, battleships King George V and Rodney, heavy cruisers Dorsetshire and Norfolk had pounded Bismarck and sent her to the bottom. The loss of Bismarck was a humiliating defeat to the Kriegsmarine and thereafter Admiral Raeder’s influence on Hitler declined; that of Donitz rose commensurately.

A number of tankers had been deployed to support and replenish Bismarck and her fleet. These were now re-tasked to support u-boats. However they were systematically sunk one by one and some captured by the British using DF information.

Another significant battle occurred on November 13 1941. U-81 (Guggenberger) was one of six u-boats tasked to shut off supplies to Tobruk, to assist Rommel’s operations in Libya. On that afternoon, Task Force H sailed right at U-81 at 19 knots. Raising to periscope depth at 4.29pm, Guggenberger fired all four bow torpedoes from long range – two at HMS Malaya and two at HMS Ark Royal. Guggenberger missed Malaya, but one torpedo found Ark Royal amidships on the starboard side. The explosion sparked off a series of uncontrollable fires. Sixteen hours later on November 14, 6.13am, the Ark Royal capsized and sank. All but one crew were saved, but seventy two planes were lost onboard.

Operations in the Atlantic continued at a steady pace. Although there was a marked increase in attacks on Mediterranean convoys, Donitz was disappointed with the meager results of this campaign. Except for the Ark Royal sinking, Donitz was trying to find a way to lift the shroud of darkness which had enveloped the u-boat force. He did not have to wait long - as a whole new hunting ground was about to arise, this time far to the west.