NKK (Nihon Kokan) Tsurumi Shipyard

The NKK (Nihon Kokan) Tsurumi Shipyard was established in 1940 when Nippon Kokan K.K. (日本鋼管株式会社), Japan's first privately owned steelmaker founded in 1912, merged with the Tsurumi Steelmaking and Shipbuilding Company (鶴見製鐵造船). Located in Tsurumi-ku, Yokohama, within the Keihin Industrial Zone — one of Japan's most important industrial corridors — the shipyard became a critical facility for wartime naval vessel production.

During World War II, the Tsurumi Shipyard was heavily involved in constructing escort ships (海防艦, kaibōkan) for the Imperial Japanese Navy. As Allied submarine attacks devastated Japan's merchant shipping from 1943 onward, the Navy General Staff urgently ordered mass production of escort vessels. NKK Tsurumi received substantial orders for these ships. The yard built the lead ship of the Ukuru-class (鵜来型) escort vessels — the Ukuru — which was laid down on October 9, 1943, launched on May 15, 1944, and commissioned on July 31, 1944. Three sister ships were also constructed at the facility. Notably, NKK Tsurumi pioneered Japan's first block construction method for shipbuilding, a significant innovation that improved production efficiency. Of the four Ukuru-class vessels built at the yard, three survived the war intact; the second ship, Okinawa, was heavily damaged and settled on the bottom, and was scrapped after the war. The shipyard also built submarine chasers, including CH-18, which was laid down in 1941 and commissioned on July 31, 1941.

Key figures in the wartime production effort at NKK Tsurumi included Naval Technical Commander Kōichi Tōyama of the Navy Technical Department, who later became Nippon Kokan's vice president, and Toshio Ishii, a Tsurumi shipyard engineer and naval lieutenant (junior grade). The yard's contributions to mass-production capacity and quality earned recognition from naval authorities, who favored NKK with large orders for Type C escort ships.

The Keihin Industrial Area, where NKK's plants were concentrated, was severely damaged by Allied bombing raids in 1945. The destruction and fires that swept through the region devastated NKK's facilities, leaving only minimal rolling mill operations functional by war's end. Company president Ryozo Asano stepped down in 1946. Reconstruction began in April 1946 under new president Masato Watanabe.

The shipyard continued operations in the postwar era, building vessels for the Japan Maritime Self-Defense Force, Japan Coast Guard, and other agencies. Notable postwar achievements include construction of the Antarctic icebreaker Fuji (1965) and Shirase (1982). In 2002, NKK merged to form JFE Holdings, and the Tsurumi facility eventually became part of Japan Marine United (JMU) in 2013, continuing its shipbuilding legacy to the present day.