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Siemens T-37
Electromechanical teletypewriter - under construction

T. Typ 37 b, commonly abbreviated to T-37, was an electromechanical teletypewriter (German: Fernschreiber), developed around 1933 by Siemens & Halske in Berlin (Germany), suitable for digital 5-bit telegraphy communications networks (telex), using the ITA-2 (baudot) standard.

As the successor of the T-36, the T-37 was used in the years before, during and after World War II (WWII), on many telegraphy networks in Europe, in­cluding the public telex networks of Germany, Belgium, France, Austria and The Netherlands. A Dutch variant is shown in the image on the right.

During WWII, the machine was used extensively by the German Army for communication with all parts of the war theatre, mainly over fixed land-lines, but occasionally over the air (i.e. via radio). A variant of the machine with built-in One-Time Tape encryption, was known as the T-37/ICA.

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  • T-37
    This is the standard version of the T-37 teletypewriter.

  • T-37 ICA
    This is a special version that has been coverted for use as a One-Time Tape cipher machine. It features two large lamps on the front cover (a green one and a red one) and has a connection for an external tape reader.
T-37 ICA
The T-37 was also available as a One-Time Tape (OTT) cipher machine, or Mixer. This version is known as T-37 ICA and can be recognised by two large lamps on its cover: a green one and a red one. Furthermore, it has a connection for an external paper tape reader, of which the characters are binary xor-ed with the letters from the plaintext. It is the automated form of the On-Time Pad (OTP) cipher. When correctly applied and used with a truly random tape, it is unbreakable [2].

Callsign generator
Callsign generator of the Siemens T-37

Callsign generator of the Siemens T-37
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Callsign generator of the Siemens T-37

The T-37 is known to have been in service in the following countries:

  • Austria
  • Belgium
  • Denmark
  • German
  • Netherlands
  1. De Verreschrijvers T-37/LP, T-68/LP
    Description and operating instructions for the Siemens T-37 and T-68 (Dutch).
    Belgian Army. March 1967.

  2. Tgf 1011a, montage-, instel- en onderhoudsvoorschrift — WANTED
    Installation, alignment and maintenance manual (Dutch).
    PTT, November 1956, Issue 1.

  3. Tfg 1011b, Afbeeldingen
    Pictures, belonging to Tgf 1011a (Dutch).
    PTT, November 1956, Issue 1. 1
  1. Document kindly provioded by Gert Stam [1].

  1. Gert Stam, restored Siemens T-37 — THANKS !
    November 2017.

  2. Teleprinter Museum, Siemens telex machines
    Retrieved January 2018.

  3. Jerry Proc and contributors, T-37 ICA
    Retrieved January 2018.
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Crypto Museum. Created: Monday 15 January 2018. Last changed: Monday, 19 August 2019 - 19:40 CET.
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