A special-purpose computer designed at Bletchley Park (UK) based upon the reverse engineering of the Lorenz Cypher. The Lorenz Cypher was used by the German army to encrypt high command orders for transmission via teleprinter (the Enigma was a field-use cypher).
Once the key to a message was discovered (by the computer Colossus) the Tunny machine would be set to decrypt the message. The process took about four days from intercept to printout. The original Tunny machine was built about 1943 and scrapped after the war. In 2011 a working model was re-built at Bletchley Park where it is on display.