Towards the end of World War II the island was strongly garrisoned by both the Imperial Japanese Army (IJA) and Imperial Japanese Navy (IJN). A garrison of over 24,500 men reinforced by sixty tanks was garrisoned on Shumshu in nine locations centered around Kataoka. All coastal areas suitable for enemy amphibious landings were covered with permanent emplacements and bunkers, interconnected with underground passages and trenches. All the warehouses, power stations, and hospitals were up to underground. These defenses were manned by the IJA 91st Division, with the IJA 73rd Infantry Brigade. Miyoshino Airfield was a joint IJA-IJN airfield, located near the center of the island, and it hosted several aviation units operating various aircraft including IJN Nakajima B5N2 (Allied reporting name "Kate") and Mitsubishi G3M (Allied reporting name "Nell") and IJA Nakajima Ki-44 (Allied reporting name "Tojo") and Nakajima Ki-43 (Allied reporting name "Oscar") aircraft. Kataoka Naval Base was under the command of the IJN′s 5th Fleet and had three oil storage tanks as well as barracks and supply buildings. The base also had a seaplane facility in the harbor, and neighboring Imaizaki Airfield had a and a runway. These facilities were subject to sporadic air raids by United States Army Air Forces and United States Navy forces based in the Aleutian Islands from 1943 until the Japanese Emperor Hirohito announced the surrender of Japan on 15 August 1945.