Yokosuka Naval District The location of Yokosuka at the entance 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 warship s 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 based at Yokosuka , and the western zone 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 . 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 warship s 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 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 . At the time of the attack on Pearl Harbor in 1941 , Yokosuka Naval District encompassed the following Yokosuka was bombed by United States Navy and United States Army Air Forces aircraft in the final stages of the Pacific War , most notably during the attack on Yokosuka on 18 July 1945 , but many of its facilities were captured intact by the Allied forces . The Yokosuka area came under occupation by American forces during the occupation of Japan , and most of the facilities of the former Yokosuka Naval District were inherited by the United States 7th Fleet and are now known as United States Fleet Activities Yokosuka . A small portion of the area continues to be used by the modern post - war Japanese Maritime Self - Defense Force , which has preserved a portion of the original red brick gates .