Cracking the Enigma code has long been considered one of the key events in the Allied victory over Nazi Germany. In Enigma: The Untold Story of the Secret Capture, we discover the story of David Balme, the soldier who went aboard a German U-boat and brought back the Enigma machine.

Extract taken from Enigma: The Untold Story of the Secret Capture
By Peter Hore
Published by Whittles Publishing

Neither Balme nor telegraphist Alan Long knew anything about Enigma, but they were both intrigued by this strange looking typewriter.

‘And we both thought it looked very interesting, probably some sort of decoding machine, so I said: “Can you unscrew it?” And he [Long] had a little set of tools, very well equipped, and he unscrewed all the screws and this thing, about 2 feet by 1 foot, I suppose, was the famous Enigma machine. The Morse code on their Enigma machine would come in from Berlin on to their machine and would be immediately transposed into another code, and by pressing a button you got a different message. This was the famous Enigma coding machine, which we, the Navy, had never managed to capture before. Anyway we unscrewed it and sent it up. Quite difficult, about 2 feet by 1 foot and quite heavy, and one only had one arm for the machine and one arm for going up the ladder. Quite difficult. Anyway we got it up. Got it into one of the boats and back to HMS Bulldog. This was the first time that the British had ever got a German Enigma machine and it was worth untold gold.’

It not was, strictly, the first time that the British had ever got a German Enigma machine. Enigma had been invented in the 1920s, when it was used commercially, and it had only later been adapted by several countries to military use. Starting in 1932, Polish military intelligence had ‘broken’ German Enigma machines using reverse engineering, mathematics and material supplied by the French.

The Enigma machine consisted of a set of rotors that were driven electrically. Coding was achieving by the setting of the rotors, and each rotor had twenty-six positions, one for each letter of the alphabet. There was a choice of rotors to install (at this stage of the war the German navy used three rotors from a choice of eight). The order of the rotors could be changed, and the initial position for each could be varied. There was also a plug board, and all of this equipment was changed and set differently each day. In addition, each individual message was encrypted using an additional, three-letter key modification. The Poles devised mechanical devices for breaking Enigma ciphers, but as the Germans introduced more complexity to their Enigma machines, decryption became more and more difficult, requiring resources that the Poles did not have.

In 1939 the Poles shared their knowledge with the British and French, and, after the fall of France, Britain exploited this knowledge alone. Through German procedural flaws, operator mistakes, and capture of key tables and hardware, British codebreakers gradually mastered Enigma. At first the intelligence gained from read Enigma and other sources was known as Boniface, but from 1941 onwards it was designated as Ultra. Ultra was particularly important in the Battle of Atlantic because of the way in which the U-boats were operated.

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The war at sea and in particular the Battle of the Atlantic was profoundly changed by the secret capture Balme had made. Bletchley began to read continuously and with little or no delay the wireless traffic in the ‘home’ or Heimisch settings of German naval Enigma, which were common to most of the German surface navy and to U-boats in the Atlantic and the Mediterranean. The combined effect of these captures was to enable Bletchley to read all German naval signal traffic for June and July, including ‘officer only’ signals, concurrently with the intended German recipients.

It also gave Bletchley such an insight into the workings of Enigma that by the beginning of August ‘it had finally established its mastery over the home waters settings, a mastery which enabled it to read the whole of the traffic for the rest of the war except for occasional days in the second half of 1941 with little delay. The maximum delay was 72 hours and the normal delay was much less, often only a few hours.’

Balme’s pinch saved countless Allied ships and lives, and brought about the end of numerous U-boats and their crews. Ultimately, in the opinion of one naval historian, it led two years later to a German retreat from the North Atlantic, which was a strategic victory as important as the Battle of Midway in the Pacific and the Battle of Stalingrad in Europe.

Enigma: The Untold Story of the Secret Capture by Peter Hore is published by Whittles Publishing, priced £16.99