Not all German Army messages were encoded by Enigma. Some high-level messages were sent using teletypes fitted with their own cyphering machines; since these sent high-speed binary signals, the design of the encoders was significantly different to Enigma's (though based on the same process) and so required a separate staff at Bletchley Park. The characteristic "non-Morse" signals were called "Fish" by BP staff, and the two types of teletypes used given the names "Tunny" and "Sturgeon".
A significant break came in August of 1941 when a German operator sent a 4,000 character message, and was asked to resend it. He did so, using the same code settings, verbatim except for the first word which he abbreviated. This gave a fabulous piece of depth to the BP cryptanalysts; seeing what was essentially the same message coded two different ways on the same machine gave a crucial insight into reverse-engineering it.
At first, processing the Fish data was performed by hand, but in 1943 an electro-mechanical device named Heath Robinson (after the British equivalent of Rube Goldberg) was introduced. It was a temperamental machine, but reportedly it had the redeeming feature that it was possible to diagnose a fault by the noise it made -- or the smell, if the problem caused it to overheat and catch fire.
Turing, working informally as a consultant on Fish, made the suggestion that a device using vacuum tubes would be more reliable, flexible and faster, and as a result in 1944, Colossus Mk I was installed, in plenty of time to decode the German High Command's responses to the D-Day landings. Colossus was the first programmable computing device with a substantial memory and conditional logic, but due to official secrecy its design never directly contributed to later commercial computer designs.
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