Yokosuka Naval Arsenal

The Yokosuka Naval Arsenal (横須賀海軍工廠) traces its origins to the Yokosuka Iron Works (横須賀製鉄所), established in 1865 under the direction of French naval engineer Léonce Verny during the final years of the Tokugawa shogunate, at the instigation of the finance magistrate Oguri Tadamasa. It was in effect a modern shipyard with docks, foundries and machine shops. The Meiji government renamed it Yokosuka Shipyard (横須賀造船所) in 1871, when No. 1 dry dock was completed, and placed it under the Navy the following year; Seiki, Japan's first domestically built warship, was finished there in 1876. It became the shipbuilding department of the Yokosuka Naval District after 1884 and, merged with the ordnance works, the Yokosuka Naval Arsenal in 1903 — one of the Imperial Japanese Navy's four principal arsenals alongside Kure, Sasebo, and Maizuru.

As the arsenal closest to naval headquarters it was responsible for prototypes and technical development, and the lead ships of many classes were built there. Its capital ships included Satsuma, Japan's first domestically built battleship, the battleships Yamashiro (completed 1917) and Mutsu (1921), and the aircraft carriers Hiryū (1939) and Shōkaku (1941) — all completed before the Pacific War, contrary to the wording of this site's earlier text. During the war it built the carrier Unryū and, in No. 6 dock completed in 1940, converted the third Yamato-class hull into Shinano, then the world's largest aircraft carrier; completed in November 1944, she was sunk by a U.S. submarine ten days later on her way to Kure. The Naval Air Technical Arsenal and the Naval Engineering School stood nearby.

The wartime workforce included many conscripted workers, mobilised students and members of the Women's Volunteer Corps. The arsenal was attacked during the Doolittle Raid (18 April 1942), when a B-25 damaged the submarine tender Taigei, then in dock being converted into the carrier Ryūhō. Yokosuka was later attacked several times by carrier aircraft; a large carrier air strike on 18 July 1945 targeted the battleship Nagato in the harbour, damaging her and sinking several other vessels.

U.S. forces occupied the arsenal in September 1945 and it was officially abolished on 15 October 1945 following Japan's surrender. It became the U.S. Navy's Ship Repair Facility at Yokosuka, where the stone-built Nos. 1–3 dry docks of the 1870s and 1880s remain in use after a century and a half, the oldest modern docks in Japan. Being inside the American base, they are not normally open to visitors; Verny Park and the Verny Commemorative Museum across the water display a steam hammer from the iron works, and with other former naval facilities they form part of the "Chinjufu" Japan Heritage recognised in 2016.