United States Army , Japan United States Army , Japan ( USARJ ) consists of about 2 , 000 soldiers and is charged , during peacetime , with operating port facilities and a series of logistics installations throughout Honshū and Okinawa . USARJ participates actively with the Japan Ground Self - Defense Force in bilateral training exercises and the development of bilateral plans . It commands and supports United States Army assigned units , attached units , and augmentation forces and employs these forces in support of the commander . USARJ maintains and strengthens the credibility of deterrent power in the Pacific through maintenance of defense facilities , war reserves and operational project stocks . USARJ is headquartered at Camp Zama . As the Army Component Command to United States Forces Japan ( USFJ ) and as a Major Subordinate Command of United States Army Pacific ( USARPAC ) , United States Army Japan ( USARJ ) / I Corps ( FWD ) is responsible to provide support of Article V ( Defense of Japan ) and VI ( ensuring regional stability ) of the Mutual Security Treaty ( MST ) . It serves as a forward stationed Army command and control headquarters ; supports regional security cooperation activities with the Japan Ground Self Defense Force ( JGSDF ) for the purpose of contributing to the security of Japan and maintenance of peace and security in the Far East ; provides communities of excellence and installation operations that support Soldiers , Civilians , and their Families . United States Army , Japan consists of : History . Reorganization of U . S . forces in the Pacific in January 1953 established Army Forces Far East as the major Army command in the Far East . AFFE moved to Camp Zama , 35 miles southwest of Tokyo , in October 1953 . On 20 November 1954 , AFFE was combined with the Eighth US Army to become AFFE / Eighth US Army . In 1955 , the Eighth US Army moved its headquarters to Yongsan Garrison , Seoul , Korea , and the Camp Zama command element was designated AFFE / Eighth US Army ( Rear ) . The name , US Army Japan ( USARJ ) , first appeared on 1 July 1957 in a reorganization of US forces in the Pacific . A major change in the Army ' s command and organizational structure in the Pacific occurred on May 15 , 1972 , in conjunction with the return of Okinawa to Japanese control after twenty - seven years of administration by the United States . Under the complex reorganization that accompanied reversion , Headquarters , IX Corps , was transferred from Okinawa and collocated with Headquarters , U . S . Army , Japan , to form Headquarters , U . S . Army , Japan / IX Corps , at Camp Zama , Japan . On Okinawa , Headquarters , U . S . Army , Ryukyu Islands , and Headquarters , 2d Logistical Command , were inactivated and a U . S . Army Base Command , Okinawa , was established to command and support all Army units there and perform the theater logistic functions for United States and allied forces in the Pacific . Numerous other refinements were made to meet the dictates of operations in Southeast Asia and the gradual transition to peacetime conditions . Five subordinate commands were left within U . S . Army , Japan / IX Corps , under the reorganization : the U . S . Army Base Command , Okinawa ; the U . S . Army Supply and Maintenance Activity , Sagami ; the U . S . Army Garrison , Kanto Plain ; the U . S . Army Transportation Activity , Japan ; the U . S . Army Ammunition Depot Complex , Akizuki ; the U . S . Army Medical Activity , Japan ; and the U . S . Army Procurement Agency , Japan . Total Army strength in Japan and Okinawa was reduced slightly as a result of this reorganization . With the discontinuance of U . S . Army Pacific on December 31 , 1974 , U . S . Army Japan was designated a Major Army Command on January 1 , 1975 reporting directly to Headquarters , Department of the Army . On February 28 , 1971 , the U . S . Army Hospital , Camp Kuwae , Okinawa was transferred to the Navy and concurrently U . S . Army Medical Department Activity , Japan , was disestablished , leaving USARJ with two subordinate commands , U . S . Army Garrison , Okinawa and U . S . Army Garrison , Honshu . U . S . Army Garrison , Honshu , was re - designated the 9th Area Support Group ( PROV ) on January 16 , 1986 . The 9th Area Support Group terminated its provisional status on October 15 , 1987 , and was activated as the 17th Area Support Group . In line with the Department of the Army directed Transformation of Installation Management ( TIM ) initiative , U . S . Army Garrison , Japan was organized effective 16 Oct 2002 with the inactivation of the 17th Area Support Group and the merger of the installation management functions throughout Japan . USARJ ' s implementation of TIM also entailed the organization of the U . S . Army Host Nation Support Activity , Japan effective 1 October 2002 for consolidation of the Government of Japan funded Master Labor Contract ( MLC ) employees utilized by USARJ assigned units into a single mission career account .