As part of the US Congressional inquiry into the Japanese attack on Pearl Harbor, much classified and secret military material was made public, including the interceptions and decryption of Japanese messages encrypted with JN-25. The British side of the story, namely the work done at Bletchley Park against Enigma and Japanese codes, remained secret for decades: until 1974, when some aspects were revealed, while others only came to light in the 1990s or even the following decade.
