(cross-posted at Photon Courier)
During WWII, the British used electomechanical devices called bombes to break the German Enigma code. The bombe in its earliest form was developed by the Poles, but was considerably enhanced by the British. (The name probably came from an ice cream dessert popular among the Polish mathematicians who did the original work)
Following WWII, strict secrecy was maintained concerning the codebreaking activities, and all of the bombes were eventually destroyed. Now, a group of volunteers has reconstructed a working bombe–it may be seen at Bletchley Park, which was Britain’s main codebreaking center during the war.
The original British bombe, named “Victory,” was delivered in March 1940. It was followed by a considerably improved model named “Agnus Dei”–Lamb of God, a strange name for what was, after all, basically a weapon. Additional improvements were made throughout the war, and by May 1945 there were more than 200 machines in service.
Codebreaking, though, was by no means a purely mechanical function–it required considerable human insight and intuition. Few professional cryptanalysts were available, and those tasked with the work were mostly academics–there were many mathematicians, including the tragic genius Alan Turing, but also quite a few classicists. Bletchley also employed a large number of young women, most of whom performed operational and maintenance functions but some of whom served as cryptanalists. One of these was Mavis Lever, who was halfway through a degree in German when the war began:
I was concentrating on German romantics and then I realized the German romantics would soon be overhead and I though well, I really ought to do something better for the war effort. I said I’d train as a nurse and their response was: “Oh no you don’t. You use your German.” So I thought, great. This is going to be an interesting job, Mata Hari, seducing Prussian officers. But I don’t think either my legs or my German were good enough because they sent me to GC&CS. (GC & CS = Government Code and Cypher School)
While analyzing one enemy message, Lever noticed that it did not contain a single instance of the letter “L”–significant because, due to a peculiarity of the Enigma machine’s design, a letter could never be enciphered to itself. Following this observation, she was able to deduce that the operator must have been sending a test message, and lazily holding down the “L” key to generate a sequence of text. (Enigma advanced its coding wheels with each character, so “LLLLL” might be encoded as “JCXAT”.) Using the assumption that the message contained all “L”s, it was possible to identify the wiring and settings of this particular Enigma machine and thence to break other traffic which had been enciphered on it.
Enigma machines were used by the Italians as well as the Germans, and in early 1941 Lever and her associates broke a very long Italian naval message–the battle plan for a night attack on a British convoy. The decoded message allowed Admiral Cunningham to set a trap for the Italians at Cape Matapan, resulting in the sinking of three heavy cruisers and a destroyer, plus damage to the battleship Vittorio Veneto. Three thousand Italian sailors were killed, and the Italian Navy never really recovered from the encounter.
The breaking of Enigma messages also contributed to the destruction of the Bismarck. Years after the war, Mavis Lever took her son to see the movie Sink the Bismarck:
I saw it go down and suddenly I really did feel quite sick. I put my head down and my son said to me after a while: “It’s all right Mummy, it’s gone down.” He didn’t know. But I was thinking how awful it was that one’s breaking of a message could send so many people to the bottom. But that was war and that was the way we had to play it. If we thought about it too much we should never have been able to cope.
While it would be an overstatment to say that the decoding work won the war, it certainly shortened it considerably and saved many lives.
Each bombe was powered by a 3/4 horsepower electric motor…trivial by comparison with the 8,000 hp of a heavy bomber or the 100,000+ horsepower of a major warship. Yet in their impact on the outcome of the war, the bombes counted as much as large numbers of the more conventional weapons.
The Mavis Lever quotes are from Station X, by Michael Smith.