Siemens and Halske T52

The Siemens and Halske T52, also known as the Geheimfernschreiber ("secret teleprinter"), or Schlüsselfernschreibmaschine (SFM), was a World War II German teleprinter cipher machine. The machine and its traffic were codenamed Sturgeon by British cryptanalysts.

While the Enigma machine was generally used by field units, the T52 was an online machine used by Luftwaffe and German Navy units, which could support the heavy machine, teletypewriter and attendant fixed circuits. It fulfilled a similar role to the Lorenz SZ40 and SZ42 machines in the German Army.

The British cryptanalysts of Bletchley Park codenamed the German teleprinter ciphers Fish, with individual cipher-systems being given further codenames: just as the T52 was called Sturgeon, the Lorenz machine was codenamed Tunny.