The Sailor Who Discovered ADM Yamomoto’s Plans to Attack Midway

While working on garbled JN-25 coded messages at Fleet Radio Unit Melbourne (FRUMEL), YN2 William H. Trimblay recognized the code group “ATTACK AF.”

FRUMEL immediately forwarded the discovery to Station HYPO in Hawaii and OP-20G in Washington DC. The United States was now aware of the first part of Admiral Isoroku Yamomoto’s Battle Plan in the Pacific. The BIG question, however, was where and when will the attack take place!

The attack location and time were confirmed when the American base at Midway Island sent out a false message, deliberately using a low-grade encryption system, stating U.S. forces were short of fresh water and to send a water barge. As planned, the Japanese intercepted the message and reported to their chain of command that “AF” was short of fresh water. Navy radio intercept operators intercepted and broke the Japanese message, confirming Midway Island was the location of the attack.