Military Communications and Electronics Museum | Musée de L'électronique et des communications militaires

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Cryptologic Technology

In the past, military commanders had to choose between communications that were either secure or rapid. The introduction of radio compounded this problem as the enemy could easily intercept and understand any unencoded radio message. During World War II, manual coding systems were replaced by much faster mechanical devices. Since the 1970s, advances in electronics have almost eliminated encoding/ decoding delay.


This German cypher machine was used extensively by all German military forces in World War II. It introduced into military communications the concept of simple dependable electrical/ mechanical encoding and decoding of messages. Unfortunately for Germany, however, ENIGMA cyphers had been broken by the Allies and much of their message traffic was being intercepted and read without their knowledge. The need to break the cyphers used in this machine gave rise to the Allied development of the first electronic computing devices.

The "Heads Up"

In 1938 a Polish mechanic was employed in a German factory producing a secret signalling machine. During a Gestapo security check his nationality was discovered and he was returned to Poland. His notes, observations and a wooden mock up which he built provided the first allied technical information on ENIGMA.

By 1939, the British had a complete new ENIGMA machine in their possession BUT the key to the machine was the cypher settings. It took a team of top mathematicians a month or more to determine a single cypher setting while the settings were changed at least daily. The British Government Code and Cypher School was set up at Bletchley Park and was tasked with solving this dilemma.

The Key to "scrambling" the signal was the ENIGMA machine's individually marked rotors, each wired differently. Three or four specified rotors were used for each code setting. Further permutations were made possible using the "switchboard" on the front of the keyboard. Rotors could also be rewired to a new combination of connections.

To code or decode a message the operator had to extract from a key list which rotors to use and the switchboard combinations. The start letter at which each rotor was to be set was included in the message. Each time a key was pressed a letter was lit to show the encoded letter and a rotor in the ENIGMA rotated, changing the code for the next letter.