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Secure Communications on the Battlefield? Gary Krahn History For two days in June 1942, the fate of the U.S. Fleet (rebuilt since Pearl Harbor) hung on the meaning of two letters - AF. Between December 1941 and June 1942, the Japanese Navy under the command of Admiral Yamamoto had swept from one victory to another. Yamamoto knew it was essential to achieve victories in rapid succession. Given time, America could starve Japan of fuel. At Midway he would deal the U.S. Fleet a crushing defeat that would put it permanently out of action. On May 20, 1942 Yamamoto broadcast his plans for the final destruction of the U.S. Fleet in a series of orders to his own fleet. At the same time the U.S. Combat Intelligence Unit at Pearl Harbor started to break into the stream of five- digit code groups that concealed the admiral’s intentions. The projected battle began to emerge, however, the when and where remained hidden in mysterious letter groups that defied analysis. The key location was coded: AF. The U.S. crypto unit employed one of the oldest tricks in the book. Using a code that they knew the Japanese had already broken, they arranged for the U.S. Garrison on Midway to broadcast the news that they were short of fresh water. Two days later, Yamamoto broadcasts to his fleet, “AF is short of freshwater.” Admiral Nimitz was now able to get his fleet to Midway and surprise the Japanese. The Americans destroyed all four of the big Japanese aircraft carriers that had attacked Pearl Harbor. As Admiral Nimitz later observed: “Midway was a victory of intelligence.” Introduction On the battlefield we must have the ability to transmit information quickly and securely. Information management is a combat multiplier that is critical to impl