There is a documentary called Codebreakers: Bletchley Park's Lost Heroes made in 2011. Which is well worth a watch if you can find it. Even the guys at the top had the same problem with having to maintain secrecy long after the war. One thing the documentary mentioned is that the Germans and presumably the Japanese had no idea how far their radio signals could be picked up, monitored and broken. It is about the Lorenz (Tunny) code not Enigma, and is mainly about Bill Tutte and Tommy Flowers with testimony from Capt. Jerry Roberts who was there at the time and was the last survivor of that group. The whole lot, from Marjorie Stetson to Bill Tutte were remarkable people.
The start of the breaking of the Lorenz code started with a transmission from Athens to Vienna of 4,000 characters, which the operator was asked to repeat and he did.
Code-Breakers: Bletchley Park's Lost Heroes: Directed by Julian Carey. With Keeley Hawes, Jerry Roberts, Jack Copeland, Paul Gannon. This is a documentary about unsung heroes of World War II. In 1943, a 24-year-old maths student and a GPO engineer combined to hack into Hitler's personal...