Siemens and Halske T52

The teleprinters of the day emitted each character as five parallel bits on five lines, typically encoded in the Baudot code or something similar.

For example, if a cipher clerk erred and sent two different messages using exactly the same settings—a depth of two in Bletchley jargon—this could be detected statistically but was not immediately and trivially solvable as it would be with the Lorenz.

One such flaw was the ability to reset the keystream to a fixed point, which led to key reuse by undisciplined machine operators.

The Swedes immediately tapped the line, in May 1940, and the mathematician and cryptographer Arne Beurling cracked the two earliest models in two weeks, using just pen and paper (a feat later replicated by Bill Tutte at Bletchley Park with the Lorenz teleprinter device used by the German High Command).

[2] The telephone company Ericsson manufactured a number of T52 analogue machines[3] that could decode the messages once the key settings had been found by hand.