Chichijima, the largest island in the Ogasawara (Bonin) group, held significant strategic value for the Imperial Japanese military during the Second World War.

Its location, roughly midway between Japan and the central Pacific, made it a natural relay point for long‑range communications, weather reporting, and naval coordination.

By the late 1930s, the island had become the primary site for Japan’s long‑range radio stations in the Nanpō Shotō, forming a critical link between the Home Islands and the scattered outposts of the central Pacific.

As tensions in the Pacific increased, Chichijima’s importance grew, and it developed into the heaviest‑garrisoned island in the chain.

By 1944 the Pacific War had entered a phase defined by sustained Allied offensives and the progressive isolation of Japanese strongholds.

In the Central Pacific, U.S. forces advanced through the Marshall and Mariana Islands, capturing Saipan, Tinian, and Guam between June and August.

These operations provided airfields for B‑29 bombers, enabling direct strikes against the Japanese Home Islands.

The loss of the Marianas also contributed to the destruction of Japan’s carrier aviation during the Battle of the Philippine Sea in June 1944.

At the time of the attack on Pearl Harbor in December 1941, Chichijima hosted a substantial military presence.

Contemporary accounts indicate that an Imperial Japanese Army force of approximately 3,700 to 3,800 men formed the core of the garrison.

Alongside them were roughly 1,200 naval personnel responsible for operating the island’s naval base, seaplane facilities, radio and meteorological stations, and small craft units including gunboats, submarine chasers, and minesweepers.

The island’s defensive strength was further reinforced by a heavy artillery fortress regiment, which provided coastal defence and contributed to the broader defensive network intended to protect Japan’s eastern approaches.

The island’s civilian population, including the Oubeikei - descendants of Western settlers who had lived on the Bonin Islands since the nineteenth century - experienced increasing scrutiny as wartime controls tightened.

Japanese authorities viewed the Oubeikei with suspicion, concerned that their foreign ancestry and linguistic background might make them vulnerable to espionage or foreign influence.

Reports indicate that they were compelled to adopt Japanese names and conform to stricter cultural expectations.