Washington Naval Treaty - Cryptanalytic Influences On The Treaty

Cryptanalytic Influences On The Treaty

What was unknown to the participants in the Conference was that the American "Black Chamber" (the Cypher Bureau, a US intelligence service), under Herbert Yardley, was spying on the delegations' communications with their home capitals. In particular, Japanese communications were thoroughly penetrated, and American negotiators were able to get the minimum possible deal the Japanese had indicated they would accept, below which they would leave the Conference. As this ratio value was unpopular with much of the Imperial Japanese Navy and with the increasingly active and important ultranationalist groups, the value the Japanese Government accepted was the cause of much suspicion and accusation among Japanese between politicians and Naval officers.