When did Japan recognize American codebreaking?

Did Japan realize that American codebreakers were reading its signals?

Japanese leaders had reasons for suspicion, but they continued to explain too many compromises as coincidence instead of accepting the scale of the codebreaking threat.

The exchange asks whether Japan realized American codebreakers were reading its communications. Both sides sometimes suspected interception, but the Japanese response resembled Germany's tendency to accept coincidence as an explanation for repeated operational surprises. The lesson is institutional as well as technical: intelligence protection fails when a command does not revise its assumptions after recurring evidence of compromise.