Sturgeon, The FISH BP Never Really Caught

The German armed forces employed three different types of teleprinter cipher machines during the Second World War, the Lorenz machines SZ40 and SZ42 also called Tunny by Bletchley Park (BP), the Siemens Schlüsselfernschreibmaschine (SFM) T52, and the one-time-tape machine T43, also manufactured by Siemens. The Lorenz machines, which existed in three different models, SZ40, SZ42a, and SZ42b, are well known as the machines that were broken at BP with the aid of Colossus. The Siemens T52 existed in four functionally distinct models, T52a/b, T52c and T52ca — which was a modified version of the T52c machine, T52d, and T52e, all going under the BP code name of Sturgeon, while the Siemens T43 probably was the unbreakable machine that BP called Thrasher. The T43 machine came into use relatively late in the war and appears to have been used only on a few selected circuits. This paper will, for the first time in the open literature, explain in detail the events that led to BP breaking the Sturgeon machines. In 1964, the Swedish Under-Secretary of State Erik Boheman first revealed that Sweden had broken the German Geheimschreiber (T52) during the Second World War. [4] In 1967, David Kahn gave further details about this achievement. [16] However, it was only in 1984, when Hinsley et al. published part one of the third volume of “British Intelligence in the Second World War,” that it was officially acknowledged that BP also had experienced some success against the Siemens T52. [13] Previously, many authors had confused the T52 with the Lorenz SZ40/42 machines and had erroneously linked the Siemens T52 to Colossus. Since 1982, Donald Davies has published detailed information about the electrical and mechanical construction of the machines. [6–8] And Wolfgang Mache has through his contacts and interviews with former Geheimschreiber operators and technicians presented the evolutionary history of the Siemens T52 machines. [17–19] Apart from Sir Harry Hinsley’s and Professor Tutte’s [22] references to BP’s attack against the T52 there has so far not been any detailed account of this part of BP’s history. It is hoped the present paper will fill this void. The first section of this paper gives a short overview of the German teleprinter cipher machines and their use, followed by a short section explaining how and when BP first encountered the Sturgeon traffic. The third