British interception of Japanese diplomatic messages (coded Purple in American terms) allowed cryptographers to glean details of the conversation between the Japanese ambassador to Berlin, Oshima Hiroshi, a close confidant of Hitler. Hermann Göring and Adolf Hitler revealed to him, and thus to the British, the number of divisions and aircraft that would be involved in the surprise attack on the USSR. The contents would not be recognized as truthful by London until June 10, 12 days before the invasion.
