Promoted to rear admiral on 15 November 1940, he was commander of the 24th Air Flotilla before being appointed Chief of Staff of the 1st Air Fleet under Admiral Chūichi Nagumo in April 1941. He was involved in strategic and tactical planning and execution, including the attack on Pearl Harbor and Battle of Midway. During the aftermath of the Battle of Midway, Kusaka was able to dissuade the fleet commander and senior officers from committing suicide after the Japanese defeat. Kusaka badly sprained both ankles and was burned during the evacuation from the critically damaged "Akagi" during the battle.