The Combined Fleet came under direct command of the Imperial General Headquarters in 1937. With the start of the Pacific War with the attack on Pearl Harbor carried out by Combined Fleet's "Kido Butai" (1st Air Fleet), the Combined Fleet became almost synonymous with the Imperial Japanese Navy, under the command of admiral Isoroku Yamamoto till April 1943 when he died after his plane was shot-down by US air forces over Bougainville Island. It comprised the battleships, aircraft carriers, aircraft, and the components that made up the main fighting strength of the IJN. It was first mobilized on the whole for the Battle of Midway. After the devastating carrier losses at Midway and in the Solomon Islands campaign, the navy re-organized into a number of "Area Fleets" for local operational control of various geographic zones. The Combined Fleet then evolved into more of an administrative organization.