history · 31 May 1942 · 82 years ago
Joseph Rochefort's cryptanalytic team in Pearl Harbor, US Territory of Hawaii intercepted a radio message noting that carrier Zuikaku's air group was being transferred out of the carrier, which provided a strong hint that Zuikaku was not going to participate in the upcoming offensive. Later on the same day, Chester Nimitz informed his carrier task forces commanders that the Japanese attack would likely take place on 3 Jun 1942, and the Japanese would be operating four fleet carriers.
More history on 31 May
OnThisDay.net