A lot of people now think that Alan Turing cracked the Enigma. A lot of people like to correct those people and say that it was the Poles who truly cracked the Enigma. So we really need to correct everyone and set things straight, because it was far more nuanced than that, with far more people involved, and different versions of Enigma were cracked even earlier. If you read enough about code breaking you end up with a fuzzy timeline in your head pieced together from all the various sources. Here’s what I’ve osmosed:
During WWI the allies broke the German ciphers wide open. And straight after the war various brits rather stupidly said so. A young Winston Churchill was one of those to mention it. Some Germans took notice.
In early post-WWI Germany a young engineer called Arthur Scherbius invented the Enigma cipher machine. It was expensive so didn’t get widely adopted. It was available commercially although sales were weak, and the Italian navy (who were our allies during WWI) and the Swiss army brought it. These early Enigma variants would be met during the Spanish revolution and WWII. The German navy also brought and weakened this early Enigma too, but would supplant it with later variants before the war began.
In 1927 a brit called Hugh Foss did a cryptoanalysis and worked out how to break this early Enigma. This early Enigma had no plugboard and a long string of countries would eventually break it on their own, including Poland, France and the United States.
One of the Germans who had taken heed of the allied boast of cracking their codes was Rudolph Schmidt. When he became chief of staff to the signal corps he decided that the German army needed strong mechanical encryption. The Enigma adopted by the German army was modified to include a plugboard and the wiring order of the keys also differed. New rotors with different internal wiring were also used.
The very successful Rudolph Schmidt had an unsuccessful younger brother called Hans Thilo Schmidt. Rudolph tried to help Hans by giving him a job but Hans resented Rudolph in particular and Germany in general enough that he decided to sell the secrets of the Enigma to the French.
The French were interested, but at that early time their cryptographers thought the Enigma unbreakable and shrugged their shoulders. The French had a treaty so gave the info to their new allies the Poles. The Poles, though, were acutely interested in breaking German comms and set about it with urgency.
The Poles were getting the actual day keys from Hans via the French, but they withheld them from their cryptographers. Their cryptographers, particularly Marian Rejewski, not knowing the keys were actually known, set about cracking it from first principles and they succeeded! Their attack was based upon the repetition of the message key at the start of each message.
During the Spanish civil war the brits, lead by the WWI veteran Dilly Knox, broke the early Enigma in use by the Condor Legion as Hugh Foss had laid out a decade earlier.
However, Dilly Knox thought the much more modern Enigma used by the German military at home was unbreakable. Then, as war loomed, the Germans stopped repeating their message key at the start of each message and the Polish attack stopped working. The Poles, in desperation, showed everything they had done to their allies France and Britain. This was a revelation, and the most important thing was it showed that the Enigma had been beaten and made people seriously consider if it could be broken again. Its all about mindset!
Dilly Knox was dying of cancer but continued to contribute massively in the early years of the war. He worked on the Italian codes, which were still using the early Enigma, and he very finally broke the modified Abwehr Enigma, which was crucial to the success of the Double-Cross spy-turning system.
Dilly Knox made way for a new kind of cryptographer who had came from a mathematical background, including Alan Turing. But Alan was not alone.
