The Free On-line Dictionary of Computing (30 December 2018):

Tunny Emulator

    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.

   (2012-03-25)