Background
When did the preliminary planning begin?
Battle of Midway
Japan had attained its initial strategic goals quickly, taking the Philippines, Malaya, Singapore, and the Dutch East Indies (now Indonesia); the latter, with its vital oil resources, was particularly important to Japan. Because of this, preliminary planning for a second phase of operations commenced as early as January 1942. However, there were strategic disagreements between the Imperial Army and Imperial Navy, and infighting between the Navy's GHQ and Admiral Isoroku Yamamoto's Combined Fleet, such that a follow-up strategy was not formed until April 1942. Admiral Yamamoto finally succeeded in winning the bureaucratic struggle with a thinly veiled threat to resign, after which his plan for the Central Pacific was adopted. Yamamoto's primary strategic goal was the elimination of America's carrier forces, which he perceived as the principal threat to the overall Pacific campaign. This concern was acutely heightened by the Doolittle Raid on 18 April 1942, in which 16 US Army Air Forces B-25 Mitchell bombers launched from bombed targets in Tokyo and several other Japanese cities. The raid, while militarily insignificant, was a severe psychological shock to the Japanese and showed the existence of a gap in the defenses around the Japanese home islands as well as the accessibility of Japanese territory to American bombers. This, and other successful hit-and-run raids by American carriers in the South Pacific, showed that they were still a threat, although seemingly reluctant to be drawn into an all-out battle. Yamamoto reasoned that another attack on the main U.S Naval base at Pearl Harbor would induce all of the American fleet to sail out to fight, including the carriers. However, due to the strength of American land-based air power on the Hawaiian Islands, he judged that it was too risky to attack Pearl Harbor directly. Instead, Yamamoto selected Midway, a tiny atoll at the extreme northwest end of the Hawaiian Island chain, approximately from Oahu. Midway was not especially important in the larger scheme of Japan's intentions, but the Japanese felt the Americans would consider Midway a vital outpost of Pearl Harbor and would therefore be compelled to defend it vigorously. The U.S. did consider Midway vital; after the battle, establishment of a U.S. submarine base on Midway allowed submarines operating from Pearl Harbor to refuel and reprovision, extending their radius of operations by . In addition to serving as a seaplane base, Midway's airstrips also served as a forward staging point for bomber attacks on Wake Island.