Iwo Jima

At the time of the Japanese attack on Pearl Harbor an Army force of about 3,700–3,800 men garrisoned Chichi Jima. In addition, about 1,200 naval personnel manned the Chichi Jima Naval Base, a small seaplane base, the radio and weather station, and various gunboat, subchaser, and minesweeping units. On Iwo Jima, the Imperial Navy had constructed an airfield about 2,000 yards northeast of Mount Suribachi. Initially stationed on this field were 1,500 naval aviation personnel and 20 aircraft.

In the wake of the American seizure of the Marshall Islands and devastating air attacks against Truk in the Caroline Islands in February 1944, the Japanese military leadership conducted a reappraisal of the military situation. All indications pointed to an American drive towards the Marianas and Carolines. To counter such a move, they established an inner line of defense extending generally northward from the Carolines to the Marianas, and from thence to the Ogasawara Islands. In March 1944, the Thirty-First Army, commanded by General Hideyoshi Obata, was activated for the purpose of garrisoning this inner line. The commander of the Chichi Jima garrison was placed nominally in command of Army and Navy units in the Ogasawara Islands.

Following the American seizure of bases in the Marshalls in the battles of Kwajalein and Eniwetok in February 1944, both Army and Navy reinforcements were sent to Iwo Jima. Five hundred men from the naval base at Yokosuka and an additional 500 from Chichi Jima reached Iwo Jima during March and April 1944. At the same time, with the arrival of reinforcements from Chichi Jima and the home islands, the Army garrison on Iwo Jima had reached a strength of over 5,000 men, equipped with 13 artillery pieces, 200 light and heavy machine guns, and 4,552 rifles. In addition, the defense boasted 120 mm coast artillery guns, twelve heavy anti-aircraft guns, and thirty 25 mm dual-mount anti-aircraft guns.