Key point: Tokyo miscalculated and Washingon had broken Imperial Japan's codes.
Six months after the attack on Pearl Harbor, Admiral Isoroku Yamamoto, commander of the Combined Fleet of the Imperial Japanese Navy, sought to extend Japan’s defensive perimeter in the central Pacific with the seizure of Midway atoll, about 1,300 miles west of Hawaii. Yamamoto intended to occupy Midway and lure the U.S. Navy into a decisive battle during which his superiority in warships, particularly aircraft carriers, and planes would destroy American naval power, leaving Hawaii and possibly the West Coast of the United States open to attack.
Cracking the Japanese Naval Code
Yamamoto devised a complex plan that included a diversionary feint toward the Aleutian Islands far to the north and the division of his naval forces into a carrier group, battleship group, and landing group. Unknown to the Japanese, U.S. Navy cryptanalysts had cracked the Japanese naval code and determined that the primary target of the forthcoming Japanese offensive was Midway. Moreover, the Japanese believed they had sunk the carrier USS Yorktown during the recent Battle of the Coral Sea. However, the Yorktown had been severely damaged and underwent sufficient repairs to rejoin the U.S. Pacific Fleet in only 72 hours. Rather than facing only the American carriers Enterprise and Hornet, Yamamoto would have to contend with three carriers.
Nevertheless, Yamamoto ventured toward Midway with overwhelming superiority, including the four powerful aircraft carriers Akagi, Kaga, Soryu, and Hiryu under the command of Admiral Chuichi Nagumo. American admirals Frank Jack Fletcher and Raymond A. Spruance rendezvoused northeast of Midway and waited.
Midway’s Turning Point