IWM - Enigma and the Codebreakers

The Second World War and the Enigma machine

Before war broke out in 1939 the Germans had planned a special way of keeping their communications secret. The army, navy and air force were told to encode their messages using cipher machines called ENIGMA.

Enigma could put a message into code in over 150 MILLION MILLION MILLION different ways.

The Germans believed that no one could crack the Enigma code. But the Allies knew that if they could, they would be able to find out their enemy's military secrets.

The Enigma machine looked like a typewriter in a wooden box. An electric current went from the keyboard through a set of rotors and a plugboard to light up the 'code' alphabet.
At least once a day the Germans changed the order of the rotors, their starting positions and the plugboard connections. To decipher a message sent using Enigma, you had to work out exactly how all of these had been set.

In the 1930's Polish cipher experts secretly began to try to crack the code. Just before war broke out they managed to pass models and drawings of Enigma to British and French code-breakers.