Lorenz SZ42 – the missing motor

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The pinnacle of code-breaking at Bletchley Park can now be told in its entirety from encrypt to decrypt using the full set of 1940’s cutting edge technology following the presentation of an extremely rare Lorenz SZ42, Hitler’s “unbreakable” cipher machine, for display at The National Museum of Computing. But the machine is missing its motor and we are seeking that part.

The breaking of the top-secret Lorenz messages of German High Command is credited with shortening the war and saving countless lives. Much more complex than Enigma, the Lorenz cipher could be broken only thanks to Bill Tutte’s deduction of the architecture of a Lorenz machine without ever having seen it. As a result, the Allies were routinely able to read German High Command’s top secret messages. From 1944, with the creation of the Colossus computer by Tommy Flowers, the Allies were able to reduce the decrypt time from weeks to hours, a speed that effectively undermined the German military machine. This was especially important, for example, in the run-up to D-Day as the Allies knew that Hitler had swallowed the bait story that landings would be at Calais.

The newly arrived Lorenz SZ42 is on long term loan from the Norwegian Armed Forces Museum in Oslo. It completes the Lorenz set of Lorenz encrypt, intercept and decrypt equipment (listed below).

A Lorenz teleprinter that attaches to the encryption machine was discovered during refurbishment to be one used by the German military and not a commercial Lorenz teleprinter as originally thought.

An Ablesetafel 40 or Spruchtafel that identified the wheel settings that the operator should use on the Lorenz machine has recently been loaned to the Museum.

This Lorenz SZ42 machine is in good condition but has some missing components.

TNMOC is planning to restore the machine to working order. Many of the missing electrical components can be sourced relatively easily, but the missing drive motor is proving much more difficult.

The drive motor was manufactured by the Lorenz Company at Tempelhof in Berlin:

  • Type Number MWM 608/42
  • 220 Volt/ 50 Hz supply
  • 50 watt power consumption
  • 1500 rpm

The motor dimensions are shown in the Photo Gallery Image 3.

There are only four Lorenz SZ42 machines known to be in existence and TNMOC has been able to discover the details of the drive motor from a machine that is in the USA.

To source a replacement drive motor TNMOC is exploring several options:

  • Find an original motor which, for example, was recovered as part of a spares stock in the chaotic aftermath of World War II. This is the least likely scenario.
  • Search for an equivalent motor which may have been used in other devices, such as encryption machines and teleprinters, manufactured between 1935 and 1948
  • Have one reconstructed by a motor manufacturer


The complete set of equipment from Encrypt to Decrypt

on display daily in TNMOC Colossus & Tunny Galleries

[Encrypt] in German-occupied territories

  • Lorenz SZ42 – to generate the encrypted traffic. Only four such devices are known to exist today.
  • Ablesetafel 40 or Spruchtafel – to identify the wheel settings that the operator should use on the Lorenz machine. Only two such devices are known to exist today.
  • Lorenz teleprinter connected to the Lorenz SZ42 cipher machine – for the operator to type the message in plain text on the keyboard.

[Intercept] in Kent, England
Reconstruction of part of the Knockholt Y station – where interceptors would identify and record incoming encrypted Lorenz traffic.

  • Undulators – to record the incoming encrypted traffic on paper ‘slip’ tape for translation.
  • Perforators – to transfer the encrypted message onto five-hole punched paper tape after operators read the 'slip' by eye.

[Decrypt] at Bletchley Park, England

  • The Colossus Rebuild – to find the wheel start positions used by the Lorenz machine from the five-hole punched paper tape.
  • Teleprinter – to print the decrypted text (in plain text German).
  • Heath Robinson reconstruction -- ongoing reconstruction of the wheel-finding device that inspired Colossus.
  • Tunny machine -- to produce the final decrypt

For a more detailed story see here.

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