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Too Close For Comfort: Britain, Ultra, and the Battle of the Atlantic (1941-43)

© Joseph Sramek

In many ways, the Battle of the Atlantic was a turning point in the war. As long as the Germans continued to have the ability to sink Allied convoys, there remained a real possibility that the Allies would lose the war. [1] Without victory over the U-Boats, D-Day could not have happened. The Battle of the Atlantic, thus, was one of the more important campaigns of the Second World War.

After the war, Churchill paid tribute to this importance by writing:

The Battle of the Atlantic was the dominating factor all throughout the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea, or in the air, depended ultimately on its outcome, and we viewed its changing fortunes day by day with hope or apprehension. [2]

An organization known as Beobachtung Dienst (B-Dienst) caused much of this apprehension. Grand Admiral Karl Dönitz (the Commander-in-Chief of the German Navy and Commander of U-Boat Operations) recalled after the war that it had provided him with half of his operational intelligence. [3] It was the most successful German intelligence organization of the war.

B-Dienst was created in the 1930s as a response to Room 40's (a predecessor of Bletchey Park) successes during World War I. [4] By 1935, it had been successful enough to penetrate the British navy's most widely used code. [5] B-Dienst's work on British naval codes continued to advance throughout the remainder of the 1930s. By September 1939, it had broken the British naval codes so well that the Germans knew the positions of all ships in the British fleet. [6]

In the beginning of the war, B-Dienst had further successes in breaking British codes. The British were slow in responding to this threat, only changing the majority of their naval codes after August 1940. One code that did not change, however, was one that was most useful to the U-Boats: the British and Allied Merchants Ships (BAMS) code. [7] B-Dienst enjoyed a distinct advantage over Bletchey Park as the British were unable to break any German codes until mid-1941.

In 1941, the British Navy made a determined effort to capture Enigma machines or their parts, in order to enable Bletchey Park to break the German naval codes. In February, the Navy raided a trawler in the Arctic Ocean, which yielded spare Enigma wheels. A few months later, two weather reporting ships, the München and the Lauenburg, yielded cipher books. Then in June 1941, U-Boat U-110 was captured during a convoy battle. Before the ship was able to be sunk by the Germans, it was boarded and an Enigma machine was recovered intact. [8]

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