Portable British Typex machine, c 1930s.
© Bletchley Park Trust / Science & Society Picture Library
These machines were used to decipher intercepted messages encrypted by German Enigma machines. Throughout WWII, Germany and its allies encrypted military communiques using Enigma machines and, by 1945, over 40,000 such machines were in use. The Germans considered the Enigma code to be unbreakable, but the codebreakers at Bletchley Park in Buckinghamshire, the British forces' intelligence centre, managed to decipher the code - a feat which is said to have dramatically shortened the war.