The Bombe Machine

To fix the problem of not being able to keep up with the plethora of messages being sent every day, mathematician Alan Turing started working on the Bombe machine. The Bombe was a machine that was designed to crack the daily settings and translate the many messages sent every day. The only previous efforts to build a machine that could accomplish this task was by the Polish. The Polish Bomba was exploiting that in the German coded transmissions, “A random 3-letter message key is sent twice at the beginning of each message and that every now and then, a particular plaintext letter, yields the same ciphertext letter three positions further on.” (Crypto Museum). The Polish Bomba could get the current settings of the Enigma for the day and translate messages in approximately two hours. When Germany invaded Poland later in 1939, all the Bombas were destroyed to prevent any enemy from learning the Polish methods. In 1940, the British were aware of the concept of how the Bomba worked and were ready to develop their own version.  The Germans changed the Enigma messages to exclude the 3-letter message key to prevent any existing Bombas from relaying the messages. 

Alan Turing had decided to have the British Bombe incorporate a new method to break the code. Alan Turing’s Bombe used “cribs'' (using a part of normal text and comparing it to an encoded German Enigma message). For example, the Germans sent out an encoded weather message at the same time of day, every day. The British already knew the daily weather message, so they compared the normal text to the encoded message to find out the settings of the Enigma. The Bombe was essentially a machine that replicated up to 36 Enigmas at once to use the cribs to learn the corresponding keys and then translate the messages. Over the course of the war, approximately 200 Bombes were built and spread throughout England.

Then in February of 1942, the Germans changed the Enigmas that were used by the navy to the Enigma M4, which had an added fourth cipher wheel. This led to an immediate black out for the codebreakers. The codebreakers were unable to translate the Enigma messages from the Kriegsmarine Navy, German U-boats (submarines) could strike from anywhere, from complete stealth. It gave the Germans a large advantage in the Battle of the Atlantic, in which the British lost many lives, supply ships, and supplies due to U-boat attacks. In October of 1942, the British captured the codebooks for the Enigma M4, then the codebreakers adapted the Bombes to translate transmissions coming from the Enigma M4.