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The Enigma Encrypting Machine

1920s German engineer Arthur Scherbius invents the Enigma electro-mechanical encrypting machine. Used commercially and also by several governments, including Germany, to protect military and diplomatic communications.

1932 Polish mathematician and cryptologist Marian Rejewski partly breaks the German encryption system. French spy working in Germany acquires further information which the French passed to the Poles who are then able to read German messages and build their own replica machines.

1938 Germans develop a more complex machine which the Poles are unable to read.

1939 In July the Poles inform French and British cryptologists of their work and, after the outbreak of war, they and their equipment are evacuated to France. They also give one of their replica machines to British cryptologists.

1940 Following the fall of France, the Poles move first to Vichy, France, and then to Britain in November 1942, where they collaborate with British cryptologists.

British Decrypting Work

1938 Government Code and Cypher School (GC&CS) acquires Bletchley Park, Buckinghamshire.

1939 Recruitment of academics, mathematicians etc. by GC&CS. Separate huts established to tackle the different systems used by each of the German armed forces.

1940 HMS Griffin captures German trawler. Some naval codes temporarily broken.

1941 The Germans start using the more sophisticated Lorenz cypher machines. The British name deciphered Lorenz messages Tunny.

Alan Turing and Gordon Welchman develop a Bombe to speed up decoding procedures.

In May, a RN ship obtains Enigma machine and code books from a sinking U-boat.

In December Germany declares war on USA and American cryptologists start working with their British counterparts at Bletchley Park.

1942–43 Post Office engineer Thomas Flowers builds Colossus which implements Turing/Welchman proposals and enables Lorenz signals to be read more speedily.

1945 Government orders destruction of all machines.