Alan Turing Honoured... At Last.

[Thumpalumpacus]

IIRC one mistake the Germans made was ending each message with "Heil Hitler", which resulted in the same coded ending to most messages. Turing guessed what the closing would be and that was an important clue to reverse-engineering the cypher.

You are mistaken, I'm afraid. While they may or may not have used that salutation, the rotors were changed on a daily basis, along with the jacked connections, which with ten plugs, would provide over one hundred billion possibilities for any given message before repeating, statistically. Knowing the order of the rotors, and which types were in use on a given day, would reduce that repetition index to about six million.

But because the rotors advanced sequentially with each keystroke (either one, two, or all three depending on rotor settings) letters only repeated very rarely, and on a seemingly-random basis. "Heil Hitler" at the front of the message would get enciphered differently than the same salutation at the end.

Here's an example from an online Engima emulator:

It was a plot point in The Imitation Game but I confess I don't recall the exact context, beyond that the heavily mechanical, almost Babbage-like computer at Bletchley was way too slow to go through all the daily mathematical possibilities until they found ways to narrow it down. One of them had to do with the Heil Hitler thing. Maybe it was simply made up, IDK.

According to the following post on Quora, the Heil Hitler thing was probably a bit of legend, but that habitual formatting of messages did create opportunities to exploit.

https://www.quora.com/Did-the-inclusion-...nigma-code

As noted above, even the time it took to send a message was important. The longer the signal, the better the radio-triangulation that informed DF tracking of subs. I know of a few messages with "Heil Hitler" at one or the other end, but it was not an everyday practice.