Oppama Naval Air Technical Arsenal

The Oppama Naval Air Technical Arsenal traces its origins to 1912, when the Imperial Japanese Navy established the Committee for Naval Aeronautical Research (海軍航空術研究委員会) at Yokosuka. In 1916, the Yokosuka Naval Air Group (横須賀海軍航空隊) was formally created at Oppama — the very first naval aviation unit in Japan — tasked with pilot training, aircraft evaluation, and tactical research.

From 1918, extensive land reclamation work transformed the coastal area around Natsushima (夏島) into the Oppama Airfield, completed in 1926 with a rectangular complex covering approximately 126 acres. Adjacent to the airfield, the Naval Air Arsenal (海軍航空廠) was established in 1932, consolidating aircraft design, testing, and limited production under one command. On 1 April 1939, the facility was reorganized as the Naval Air Technical Arsenal (海軍航空技術廠, Kaigun Koku Gijutsu Sho), commonly abbreviated as "Kugisho" (空技廠).

The arsenal became the nerve center of Japanese naval aviation technology. Its engineers designed a succession of combat aircraft bearing the manufacturer designation "Y" (for Yokosuka), including the D4Y Suisei (Judy) dive bomber, the P1Y Ginga (Frances) medium bomber, and the MXY-7 Ohka rocket-powered suicide attack craft. Equally important, the facility served as the Imperial Navy's primary flight test center: virtually every prototype aircraft built by Mitsubishi, Nakajima, Aichi, and Kawanishi — including the epoch-making Mitsubishi A6M Zero — was delivered to Oppama for acceptance trials, performance evaluation, and tactical testing before being cleared for operational deployment.

By the late war period, about 1,700 staff and some 32,000 workers were employed across the arsenal's factories, wind tunnels, engine test stands, and research laboratories. The Yokosuka Naval Air Group (横須賀航空隊) stationed at the base also hosted the pioneering Preparatory Flight Training Program (予科練習生, Yokaren), established in 1930, which trained thousands of young enlisted aviators who would form the backbone of carrier air groups.

In the closing months of the war, American carrier-based aircraft attacked the Yokosuka naval area, including the Oppama complex, in 1945. Following Japan's surrender on 15 August 1945, U.S. forces occupied the facility on 30 August 1945 and redesignated it NAS Oppama. Allied technical intelligence teams catalogued and shipped numerous captured aircraft — including Zero fighters, Raiden interceptors, and experimental types — to the United States aboard the escort carrier USS Barnes for evaluation.

The base served as a major U.S. military scrapyard in the late 1940s. Fuji Motors (富士自動車) operated vehicle repair and salvage operations on the site from 1948, processing over 229,000 occupation-force vehicles by 1958. In 1961, Nissan Motor Company opened the Oppama Plant on the former arsenal grounds, which has served as Nissan's "mother factory" and pioneered innovations including the production of the Nissan LEAF electric vehicle. The Oppama Plant occupies approximately 547,600 m² at 1 Natsushima-cho, Yokosuka — the same land where Japan's naval aviation was born.