Hmm..
no idea on this one..

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That sounds like a guess.  If it was, it was a really good guess.  By the time of planning for operation Overlord, the Japanese JN-25 code had been broken and was routinely read.  However the Japanese  never knew that, although some lower-level officers suspected JN-25 was cracked after the Yamamoto ambush, but the powers-to-be dismissed that notion.

Anyway, the Germans were sharing with the Japanese Embassy in Berlin it's disposition of defenses along the French/Belgium coast to defend against an allied invasion.  And the Japanese Embassy was dutifully  sending to Tokyo that information.  And the allies were eagerly reading those messages.

Ah dang! I knew the answer to this one! I remember reading about it in The Wotan Mission by Leo Kessler (Charles Whiting). They had a big submarine and helped with supplies and codes!



A.

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Just to point out that not all the codebreakers at Bletchley Park were British by any means. At its peak it was staffed by thousands of people from all walks of life & many different nationalities. There was a Japanese decoding section at Bletchley staffed by a large proportion of American codebreakers. Due to the large number of characters in the ordinary written language I've always thought that decoding Japanese messages must have been far more difficult than German or any other European language. Come to that I could never visualise a standard Japanese typewriter or keyboard.

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The D-Day Invasion of Normandy in 1944 was a combined Allied operation planned by American & British military experts with an American general in overall command. Every piece of intelligence would have been vital to its success wherever it came from.

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I don't know the 'purple machine' you refer to but this might be similar to the Enigma codes. The Allies already had a working example of the machine at Bletchley Park by 1940 but this wasn't much use without the codes. These were changed every day & had to be planned in advance so both the sender & receiver could use the correct daily code without which the coded message could not be deciphered by anyone except the person who sent it. This is where those codebooks come into it as the Enigma machine itself was automatic. I got most of my knowledge on this subject from a recent visit & guided tour of the once top secret 'Station X' codebreaking establishment at Bletchley Park where most of this work was done throughout WWII. http://www.bletchleypark.org.uk/

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Interesting. At first sight it has certain similarities to the Enigma machine but the principle it works on is not quite as easily understood, not by me anyway. The Enigma machine is beautiful in its simplicity & also very effective. I'm no cipher expert & have enough problems doing a crossword myself.

but yes, the basic principle of all the cryptographic gear used at the time was the same.

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I don't know the facts in this specific case as I'd not heard of it before but it's quite likely that those messages you refer to were passed direct to the Japanese section at Bletchley Park for deciphering. As I pointed out earlier, this included a large American contingent. I only discovered this during my recent visit as it was never common knowledge. Everything done at Bletchley during WWII was classified as Top Secret & some still is today. Lack of knowledge of what was actually achieved there (like the development of the first electronic computer) has led to many misconceptions since the war. All equipment & documents were destroyed soon after the end of WWII to prevent it falling into the hands of a potential enemy. I don't expect this is unique by any means & there are some things that will never be revealed, at least during my lifetime.

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Woody. I should remind you that this was a combined operation. The invasion & liberation of Europe would have been impossible without the considerable contribution of American forces & equipment and I imagine intelligence. It's quite natural that any intelligence would be passed on to the appropriate area without worrying if this happened to be American or British or even Russian if affected them. It's also quite likely that those Japanese messages were deciphered at Bletchley Park as this was in the area involved & also the centre of Allied codebreaking throughout WWII. The intelligence belonged to the Allied effort & not one country & I suspect it was all passed through the same chain of command to whoever was responsible for distributing it.

I realise that inter-service rivalry caused a lot of problems during WWII & have no doubt this also applied to international cooperation but it would have been so much easier without these petty squabbles. We were all on the same side.

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There were two very good reasons the Americans came to Bletchley Park. First the establishment was already set up with the most advanced equipment available for deciphering coded messages. There were probably a lot more Japanese speakers in America (including Japanese Americans) than in Britain or anywhere except Japan. This would obviously be a big advantage in deciphering Japanese codes as they would not have to learn a very complex & difficult language in order to understand what they were doing. The establishment was not set up on a national basis & people from many different nationalities worked alongside each other to achieve a common aim. The defeat of the enemy. This was a great achievement & fine example of international cooperation.

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Indeed & this is often forgotten or not realised.

It's also not commonly known that the British & other governments were offered the Enigma machine soon after it was first invented but turned it down as they saw no practical use for it. It was originally intended for commercial use against industrial espionage & available to any large company. Only the Germans took advantage of it for military use.