"TUNNY" (Lorenz SZ-40/42)

According to the National Cryptologic Museum, the Tunny and Sturgeon machines (referred to by American cryptologists as the "fish" machines) were both on-line cipher machines, which meant that a message could be simultaneously enciphered and transmitted, thus saving a great deal of time.

When the British first encountered the Schlusselzustz 40 (SZ40) in 1941, they nicknamed the machine Tunny. The German Army used the SZ40 , manufactured by the German firm Lorenz for high level communications.  It provided on-line encrypryption and decryption of messages and was capable of handling large volumes of traffic at high speed.

Although a British cryptanalytic attack made considerable progress, the results were far slimmer than against the Enigma, both because the difficulty of attack yielded fewer breaks, and because there was a lot less traffic sent over these systems.

One can only admire the great workmanship and the mechanics of this Tunny machine which is on display at the National Cryptologic Museum.  (Photo by Jerry Proc)
An example of the Lorenz Sclusselzinsats SZ42 "chiffermachine" held by the Norwegian Armed Forces Museum in Oslo, Norway. Very often, machines are discovered in a condition like this and it takes many, many hours of dedicated work by a restoration specialist to get the machine to look factory new. (Photo courtesy of Reidar Olsen)

Frode Weierud explains the markings "emf" and "emo" seen on the covers of the printer magnets. "The SZ40 and SZ42 machines were cipher attachments that where placed in the telegraph circuit between a distant station (cipher attachment with teleprinter) and the local teleprinter. This meant that the SZ40/42 needed two receivers and two transmitters. The EMO and EMF are the receiving magnets respectively for the local teleprinter and distant cipher attachment/teleprinter.

EMO means Empfangsmagneten der Ortsfernschreibmaschine (Receiving magnets for the local teleprinter), while EMF means Empfangsmagneten der Fernschreibmaschine (Receiving magnets for the teleprinter) which here, refers to the receiver for the signals coming from the distant machine.

Front view
Right side
Left side
Detail on the meter face. Zu schnell = too fast. Zu langsam = too slow.
Closeup of the first four rotors.
All photos in this table by Ralph Simpson

Contributors and Credits:

1) Frode Weierud <Frode.Weierud(at)cern.ch>
2) Reidar Olsen, Norway.  E-mail: <trolok45@c2i.net>
3) Ralph Simpson <ralphenator(at)gmail.com>

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April 26/12