“But in every case the Japanese concluded since their code was unbreakable it couldn’t have been code breaking. So, they blamed their disasters on spies, bad luck, anything other than American intelligence reading their radio traffic.”
The Brits did the same to the German codes and keep their successes quiet for decades. The Nazis never figured it out.
I seem to recall that the Brits would let German flights in over England every once in awhile so the Germans wouldn’t think that the radar was working. Radar was brand new at the time.