An early strategic plan by Isoroku Yamamoto involved the occupation of the western Aleutians and Midway Island as a 'decoy' to lure the United States Pacific Fleet away from Pearl Harbor so as to effect the complete destruction of the Hawaiian base before reconstruction efforts could take hold. However, the Aleutians campaign meant that fewer ships could be devoted to the Battle of Midway, a turning point during World War Two. The United States armed forces had broken the Japanese communications code, and were able to learn of the Japanese plan to attack the Aleutians by May 21, 1942. The Imperial Japanese Navy's plan was to attack and hold Attu and Kiska for future use, while inflicting damage on Dutch Harbor and Adak. Once the United States Navy learned of the plan, Admiral Chester W. Nimitz sent a third of his Pacific Fleet to the Aleutian Islands, under orders to hold Dutch Harbor at all costs.