Numazu Naval Arsenal

The Numazu Naval Arsenal (沼津海軍工廠) was an important Imperial Japanese Navy manufacturing facility established in June 1943 in Numazu City, Shizuoka Prefecture. The arsenal was built on a vast tract of land north of Numazu Station on the JR Tokaido Line, extending into the former Kanaoka Village (金岡村) of Sunto District. Residents of the Sawada and Kumado districts were forcibly relocated to make way for construction.

The facility specialized in the production of electronic warfare and detection equipment critical to the Imperial Navy's operations. The wireless division (無線部) manufactured radar equipment (電波探信儀), while the aviation wireless division produced aviation communications systems. At its peak, the arsenal employed approximately 20,000 workers, including large numbers of students mobilized from middle schools throughout Numazu and Shizuoka Prefecture under Japan's wartime National Mobilization Law. The facility was commanded by Rear Admiral Shōzaburō Nakajima (中嶋省三郎), who was promoted to Vice Admiral in November 1943 and served from the arsenal's opening on June 1, 1943 until October 15, 1945.

The presence of the Numazu Naval Arsenal, along with numerous other small and medium-sized military factories in the city, made Numazu a significant target for Allied strategic bombing. The city endured eight separate air raids during the war. The most devastating came on the night of July 17, 1945, when 130 B-29 Superfortress bombers of the USAAF 20th Air Force, 58th Bombardment Wing dropped 9,077 incendiary bombs totaling 1,039 tons on the city. The firestorm destroyed 9,523 buildings and killed 274 people. Over the course of the entire war, total casualties reached 322 killed, 634 wounded, and 11,883 homes destroyed. American post-war assessments concluded that 89.5% of Numazu had been totally destroyed.

After Japan's surrender in August 1945, a GHQ inventory of the arsenal revealed 569 kilograms of silver blocks stored under Imperial Navy management. The site was returned to Numazu City and initially converted to agricultural use, though the extensive concrete paving of the former factory grounds made reclamation difficult. From the 1950s onward, rapid urbanization transformed the area. Major corporations including Fujikura Electric Wire (now Fujikura Ltd.) and Ricoh established factories on the former grounds. Several schools — Seikei High School, Tōyō High School, and Numazu Municipal Fifth Middle School — were also built on the site.

Today, the former arsenal grounds bear little physical trace of their wartime past. Nearby, the Naval Technical Research Institute Monument (海軍技研址の碑) in Shimokaganugi commemorates the related Navy acoustic research facility that operated in the area from 1941, conducting research on submarine detection equipment and underwater listening devices. Annual peace education tours organized by the Numazu City Meiji Historical Materials Museum visit wartime sites throughout the city, helping preserve the memory of the arsenal and the devastating air raids it attracted.