When did WWII code-breaking become general knowledge?

[Little_Nemo]

The United Kingdom and United States were breaking Axis codes during World War II which had a significant impact on military operations. Obviously this code breaking was a secret during the war.

How long after the war was it before this code-breaking became general public knowledge?

[ctnguy]

The fact that Allied cryptanalysts had broken the German Enigma machine was first revealed in F. W. Winterbotham’s book The Ultra Secret, published in 1974. (Winterbotham had been responsible for the distribution of intelligence information derived from Enigma intercepts.) Evidently after the war the British government distributed captured Enigma machines to ex-colonies, and wanted the fact that the cipher had been broken to stay secret.

The American break of the Japanese “Purple” cipher was apparently revealed during the post-war Congressional hearings about Pearl Harbor in 1945 and 1946.

[robert_columbia]

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[Francis_Vaughan]

There were two codes broken in WW2 - the enigma codes are probably the most famous, however the breaking of the German High Command codes - using the Colossi - was not known until the US government declassified documents that mentioned it in 1996, and then the UK government finally declassified the information in 2000. (The General Report on Tunny.)

For some reason, many people think that the Colossi was used to break the Enigma codes, which they weren’t. Enigma was broken by the Bombe machines, on both sides of the Atlantic. The Tunny codes (as the UK referred to the German High Command codes) were not broken on a regular basis until near D-Day, and it was those that relied upon the Colossi. One critical reason for the very late declassification of this is that at least two Colossi remained in operation (although they were removed from Bletchly Park) until 1960. They were probably used to decrypt communications made by countries that still had access to the German machines. This may have included Soviet states.

[ticker]

From the Bletchley Park web site:

For decades, the codebreakers would remain silent about their achievements. It was not until the wartime information was declassified in the mid-1970s that the truth would begin to emerge. And the impact of those achievements on the outcome of the war and subsequent developments in communications still has not been recognised fully.

[tellyworth]

@Francis_Vaughan

There were two codes broken in WW2

British codes were broken by the Germans too. It’s described in detail from the British point of view by Leo Marks in his excellent memoir, Between Silk And Cyanide.

(eta: yeah I know that’s not what you meant, just mentioned it as an aside).

[Hari_Seldon]

At least one of the Bletchley Park codebreakers, Peter Hilton who died during the past year, always refused to say a word about his work, saying he was sworn to secrecy in perpetuity. He was a mathematician whom I knew moderately well.

[andyleonard]

@Hari_Seldon

At least one of the Bletchley Park codebreakers, Peter Hilton who died during the past year, always refused to say a word about his work, saying he was sworn to secrecy in perpetuity. He was a mathematician whom I knew moderately well.

I believe this is the standard circumstance and one of the reasons there’s not a lot of intel around the topic. My parents met while working on Japanese codes at Pearl and they refused any conversation about what they were doing or what they knew until they died. Whatever the Navy had them sign must have had a lot of weight.