Yokosuka Naval District

Yokosuka Naval District (横須賀鎮守府, Yokosuka chinjufu) was the first of four main administrative districts of the pre-war Imperial Japanese Navy. Its territory included Tokyo Bay and the Pacific coasts of central and northern Honshū from the Kii Peninsula to Shimokita Peninsula. Its headquarters, along with most of its installations, including the Yokosuka Naval Arsenal, were located in the city of Yokosuka, which constituted the Yokosuka Naval Base.

The location of Yokosuka at the entrance to strategic Tokyo Bay was recognized of critical importance by the Tokugawa shogunate and early Meiji government. In 1866, the Tokugawa shogunate government established the Yokosuka Seisakusho, a military arsenal and naval base, with the help of foreign engineers, including the French naval architect Léonce Verny. The new facility was intended to produce modern, western-style warships and equipment for the Tokugawa navy. After the Boshin War and the Meiji Restoration, the new Meiji government took over control of the facility in 1871, renaming it the Yokosuka Zosenjo (Yokosuka Shipyards). In August 1876, the Imperial Japanese Navy was organized into eastern and a western strategic zones, with the eastern zone Tōkai chinjufu (東海鎮守府) based at Yokosuka, and the western zone Saikai chinjufu (西海鎮守府) based at Nagasaki. However, for ease of communications with naval headquarters in Tokyo, the Tōkai Naval District was relocated to Yokohama in September 1876.

With the reorganization of the Imperial Japanese Navy in April 1886, Japan was divided into five naval districts for recruiting and supply, and the headquarters for the Tokai Naval District was relocated back to Yokosuka, becoming the Yokosuka Naval District, and the Yokosuka Naval Arsenal was placed under its command. As with all naval districts, it was under the direction of the Navy Ministry during peacetime, and came under the command of the fleets stationed within the district in time of war.^[1] A Bureau of Torpedo Warfare was established at Yokusuka in June 1885. In a further administrative re-organization of the Japanese Navy in 1889, Yokosuka was designated as the “First Naval District” (第一海軍区, dai-ichi kaigunku), and its harbor was dredged, a breakwater extended and docking facilities for warships were increased. A Bureau of Mine Warfare was also established. In 1893, schools for naval mechanical engineering, torpedo warfare and naval artillery were established. Schools for naval engineering, and for mine warfare followed in 1907 and a naval medical center in 1908. Naval aviation facilities were established in June 1912, followed by a wireless communications facility in April 1913.

On January 14, 1917, the armoured cruiser Tsukuba exploded and sank in Yokosuka port in an accident. The Naval Construction Department was established in 1921. In June 1930, a Naval Communications School was established, but the Naval Mine School was made independent of the naval district. A Naval Aviation School was established in April 1934.

• United States Fleet Activities Yokosuka
• Japan Maritime Self-Defense Force#District Forces