Isoroku Yamamoto - December 1941 To May 1942

December 1941 To May 1942

With the American Fleet largely neutralized at Pearl Harbor, Yamamoto's Combined Fleet turned to the task of executing the larger Japanese war plan devised by the Imperial Japanese Army and Navy General Staff. The First Air Fleet proceeded to make a circuit of the Pacific, striking American, Australian, Dutch and British installations from Wake Island to Australia to Ceylon (now Sri Lanka) in the Indian Ocean. The 11th Air Fleet caught the American 5th Air Force on the ground in the Philippines hours after Pearl Harbor, and then proceeded to sink the British Force "Z" (battleship HMS Prince of Wales and battlecruiser HMS Repulse) underway at sea.

Under Yamamoto's able subordinates, Naval Lieutenant-Generals Jisaburō Ozawa, Nobutake Kondō and Ibō Takahashi, the Japanese swept the inadequate remaining American, British, Dutch and Australian naval assets from the Netherlands East Indies in a series of amphibious landings and surface naval battles that culminated in the Battle of the Java Sea on 27 February 1942. With the occupation of the Netherlands East Indies, and the reduction of the remaining American positions in the Philippines to forlorn hopes on the Bataan Peninsula and Corregidor island, the Japanese had secured their oil- and rubber-rich "Southern Resources Area".

By late March, having achieved their initial aims with surprising speed and little loss (albeit against enemies ill-prepared to resist them), the Japanese paused to consider their next moves. Yamamoto and a few Japanese military leaders and officials waited, hoping that the United States or Great Britain would negotiate for an armistice or a peace treaty to end the war in their favor. But when the British, as well as the Americans, expressed no interest in negotiating with Japan for any cease fire, the Japanese thoughts turned to securing and protecting their newly seized territory, and acquiring more with an eye toward additional conquest and/or attempting to force one or more of their enemies out of the war.

Competing plans were developed at this stage, including thrusts to the west against India, the south against Australia and the east against the United States. Yamamoto was involved in this debate, supporting different plans at different times with varying degrees of enthusiasm and for varying purposes, including "horse-trading" for support of his own objectives.

Plans included ideas as ambitious as invading India or Australia, or seizing Hawaii. These grandiose ventures were inevitably set aside as the army could not spare enough troops from China for the first two (which would require a minimum of 250,000 men), nor shipping to support the latter two. (Shipping was allocated separately to IJN & IJA, and jealously guarded.) Instead, the Imperial General Staff supported an army thrust into Burma in hopes of linking up with Indian Nationalists revolting against British rule, and attacks in New Guinea and the Solomon Islands designed to imperil Australia's sea line of communication with the United States. Yamamoto agitated for an offensive decisive battle in the east to finish off the American fleet, but the more conservative Naval General Staff officers were unwilling to risk it.

On 18 April, in the midst of these debates, the Doolittle Raid struck Tokyo and the surrounding areas, galvanizing the threat posed by the American aircraft carriers in the minds of staff officers, and giving Yamamoto an event he could exploit to get his way as further debate over military strategy came to a quick end. The Naval General Staff agreed to Yamamoto's Midway (MI) Operation, subsequent to the first phase of the operations against Australia's link with America, and concurrent with their own plan to seize positions in the Aleutian Islands.

Yamamoto rushed planning for the Midway and Aleutians missions, while dispatching a force under Naval Major-General Takeo Takagi, including the Fifth Carrier Division (the large, new carriers Shōkaku and Zuikaku), to support the effort to seize the islands of Tulagi and Guadalcanal for seaplane and airplane bases, and the town of Port Moresby on Papua New Guinea's south coast facing Australia.

The Port Moresby (MO) Operation proved an unwelcome setback. Although Tulagi and Guadalcanal were taken, the Port Moresby invasion fleet was compelled to turn back when Takagi clashed with an American carrier task force in the Battle of the Coral Sea in early May. Although the Japanese sank the American carrier USS Lexington and damaged the USS Yorktown (CV-5), the Americans damaged the carrier Shōkaku so badly that she required dockyard repairs, and the Japanese lost the light carrier Shoho. Just as importantly, Japanese operational mishaps and American fighters and anti-aircraft fire devastated the dive bomber and torpedo plane formations of both Shōkaku's and Zuikaku's air groups. These losses sidelined Zuikaku while she awaited replacement aircraft and aircrews, and saw to tactical integration and training. These two ships would be sorely missed a month later at Midway.