At the outbreak of the Pacific War, Harada was a Mitsubishi A6M Zero pilot assigned to the aircraft carrier "Sōryū", which formed part of the 1st Air Fleet. In this role, he took part in the 1st Air Fleet's series of operations during the initial months of the war. On 7 December 1941, he flew protective patrols over the fleet during the Attack on Pearl Harbor, and did not see any combat. Harada also escorted the aircraft which attacked the Australian port of Darwin on 19 February 1942. During the Indian Ocean raid, he was confirmed to have shot down three British fighters over Colombo on 5 April, and claimed another two as "probables". Four days later, he downed two British Bristol Blenheim light bombers which were attempting to attack the Japanese fleet.