Japanese failure to recognize their naval codes had been broken
The ability of the United States to decipher Japan’s most crucial naval communications led to several defeats of the Japanese during Second World War, including the crucial victory at the Battle of Midway. The knowledge of the Japanese plan, including the simultaneous operations in the Aleutians being a diversion, enabled Admiral Chester Nimitz to plot an ambush. American aircraft carriers were sent to lie in wait for the Japanese and Midway’s defenses were bolstered. The Japanese suffered their first major defeat as a result of the battle, bolstering American morale, and crippling the Japanese carrier strike forces. The Japanese under Admiral Yamamoto was forced to withdraw.
The ability to read the Japanese mail, so to speak, also led to the Japanese losing their most respected naval leader in 1943. US Navy code breakers were able to obtain Yamamoto’s itinerary during a tour of the Solomon Islands in April. Armed with the information, which included the type of aircraft in which Yamamoto was travelling, US Army Air Force fighters were dispatched to intercept the Admiral. The mission was a planned aerial assassination. Yamamoto was shot down on April 18, 1943, and was killed either during the attack or in the subsequent crash of the aircraft, in heavy jungle on the island of Bougainville. The American decryption of Japanese code continued throughout the war.