/// It had always been rumoured that Bletchley Park knew of the attack and the information was withheld on the instructions ot Churchill.//
yeah like the attack on Coventry - there are quite a few books on the Brits and Japanese codes. These were book codes and were solvable and solved with "depths" -
which the Brits were doing and the code used was JN 25 I think
https://en.wikipedia.org/wiki/Japanese_naval_codes
The Americans had solved the Japanese purple code ( diplomatic ) which they then ignored but did not carry details of Pearl Harbour unsurprisingly
When the Japanese over ran the code stations ( they did a lot of over funning up to 1944) the code gairls just picked up their books and pencils and went elsewhere.
When the one purple machine was recovered from the J embassy in Berlin ( burnt out ) it was JUST as the american engineers had reverse engineered. ( separate rotors for consonants and vowels and based on telephone switching)
The imperial codesters didnt even think the allies wd attmept to break their codes and were planning to massacre the POWs because they 'must' have been communicating with the invasion forces. Sep 1945