Yokosuka Naval Air Technical Arsenal

The Yokosuka Naval Air Technical Arsenal (横須賀海軍航空技術廠, Yokosuka Kaigun Kōkū Gijutsu-shō), commonly abbreviated as Kūgishō (空技廠), was the Imperial Japanese Navy's central facility for aircraft design, testing, and aviation technology research. Located in the Oppama district of Yokosuka City, Kanagawa Prefecture, on the western shore of Tokyo Bay, it was one of the most important military research establishments in wartime Japan.

The arsenal traces its origins to the aircraft division of the Yokosuka Naval Arsenal. On April 1, 1932, this division was reorganized as the independent Kaigun Kōkūshō (Naval Air Arsenal). On April 1, 1939, it was further reorganized and renamed Kaigun Kōkū Gijutsu-shō (Naval Air Technical Arsenal), reflecting its expanded role in advanced aviation research and weapons development. The facility employed a large technical workforce and maintained close ties with the adjacent Yokosuka Naval Air Group at Oppama airfield, which served as the testing ground for new aircraft designs.

The arsenal designed numerous aircraft that saw extensive service during World War II. Among the most notable were the D4Y Suisei (Comet, Allied code name 'Judy'), a high-speed carrier-based dive bomber that became one of the Navy's primary strike aircraft; the P1Y Ginga (Milky Way, 'Frances'), a twin-engine land-based bomber; and the E14Y (Allied code name 'Glen'), a small reconnaissance floatplane designed to operate from submarines. Aircraft designed at the arsenal were designated with the manufacturer code 'Y' for Yokosuka, though mass production was carried out by companies such as Aichi, Nakajima, Kawanishi, and others.

Perhaps the arsenal's most infamous creation was the MXY-7 Ohka (Cherry Blossom), a purpose-built rocket-powered kamikaze aircraft developed in late 1944. Designed by Ensign Mitsuo Ohta and engineered at the arsenal, the Ohka was a piloted flying bomb carried beneath a Mitsubishi G4M 'Betty' bomber and released near its target. Powered by three solid-fuel rocket motors, it could reach speeds over 900 km/h in its terminal dive. The weapon was first deployed in combat during the Battle of Okinawa in spring 1945, where it sank the destroyer USS Mannert L. Abele and damaged several other Allied vessels. American forces nicknamed it 'Baka' (Japanese for 'fool').

In the final year of the war, anticipating American bombing raids, the arsenal began constructing an extensive network of underground tunnels and caves to shelter workers and continue production. By mid-1945, part of the workforce was living and working underground. After Japan's surrender on August 15, 1945, staff at the arsenal were ordered to destroy documents and evidence, much of which was burned and dumped into the sea. The facility was seized by Allied occupation forces, and the Yokosuka Naval Arsenal was officially abolished on October 15, 1945. The former Oppama site later became the location of Nissan's Oppama automobile manufacturing plant, which began operations in 1961.