US Army Japan (USARJ)/I Corps (Forward)
US Army Japan (USARJ)

US Army Japan (USARJ) is the Army Component Command to the subordinate unified command, US Forces Japan (USFJ) and is a major subordinate command of US Army Pacific (USARPAC). USARJ has full coordination authority with USFJ and other service component in Japan on US Army matters. The mission of USARJ includes support US Pacific Command (PACOM) war plans and operational requirements; maintaining a bilateral relationship with the Japanese Ground Self Defense Force, providing a senior leader for immediate interface and coordination with Japanese forces/staff as needed; and executing an active bilateral engagement and exercise program.

The strategic geographic location of Japan provided the US an excellent location for forward-basing, enabling power projection forces in the event of contingencies. Combined with the existing agreements the US had with Japan for basing rights for both air and sea forces, the US Army in Japan was capable of a greatly expanded logistical support role throughout the Pacific theater. Japan occupied a key strategic location in the Pacific, which was vitally important to the US both economically and militarily. US forward presence in Japan was vital to ensuring access to the strategic location.

The US Army's forward presence in Japan enabled it to meet US bilateral engagement responsibilities under the Mutual Security Treaty and the Defense Guidelines to defend Japan from outside aggression in wartime, and to provide deterrence and stability in peacetime. It also demonstrated the US commitment to other allies and friends in the Pacific. Being in Japan, approximately 5,000 nautical miles closer to potential trouble spots than the West Coast of the US, meant USARJ and the 9th Theater Support Command could respond to crises and support regional contingencies as a strategically located base and staging area.

USARJ and 9th Theater Support Command had distinct command relationships. USARJ was a service component of USFJ, which was itself a sub-unified command of PACOM. At the same time, USARJ was a major subordinate command of the USARPAC. Although 9th Theater Support Command had a presence in Japan, it was a separate unit with missions and functions both in and out of Japan. Like USARJ, it is an major subordinate command of USARPAC with its commitment to Japan through its leadership unified with that of USARJ.

Japan was a generous US defense partner, providing in excess of $5 billion annually for labor cost sharing, utilities, facilities improvement and other related costs. The Government of Japan also provided rent-free facilities and support by a highly skilled, dedicated Japanese national work force to offset the limited number of Army personnel assigned to Japan.

The origins of United States Army Japan trace back to the formation of Army Forces Far East (AFFE) in Manila, Philippiines on 26 July 1941. Commanded by General Douglas MacArthur, AFFE moved to Melbourne, Australia after the fall of the Philippines to Japanese forces in Spring of 1942. General MacArthur served as the commanding general of AFFE and the Allied Supreme Commander of the Southwest Pacific Area (SWPA). AFFE served as the administrative headquarters for all Army forces in the Southwest Pacific from 1943 to June 1945. Near the end of World War II, the AFFE headquarters became part of General Headquarters, US Forces, Pacific. After the war AFFE was attached to General Headquarters, Far East Command, based in Tokyo. In June 1950, AFFE moved to a new headquarters in Yokohama, still attached to Headquarters, Far East Command.

Reorganization of US Forces in the Pacific in January 1953 established AFFE 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 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. USARJ and 5 other Pacific elements came under the command of US Army Pacific (USARPAC) during a reorganization completed in January 1960. During the next 25 years USARJ's area of responsibility and span of control continued to grow. In 1963 USARJ acquired the US Army Depot Command, Japan, as a major subordinate command. This was followed by US Army Garrison, Japan, which had the mission of providing station-type support to Headquarters, USARJ and its components.

Okinawa reverted to Japanese national control on 15 May 1972 and USARJ assumed an even greater role as it acquired control of the mission and functions of the former Okinawa Command, US Army Ryukyu Islands. Headquarters, IX Corps was also merged with USARJ to form USARJ/IX Corps. In July 1974, a reorganized USARJ reduced its subordinate commands from 7 to 3.

On 30 August 1990, USARJ was added to the forces under USARPAC. While many major command responsibilities previously performed by USARJ were assumed by USARPAC, USARJ continued as the Army component to US Forces Japan (USFJ), one of 4 US Pacific Command (PACOM) sub-unified commands. As such, it was the executive ageny for all bilateral activities with the Japan Ground Self Defense Forces. It was tasked to develop contingency plans, war plans, and bilateral defense plans.

The 9th Theater Support Command was officially reactivated as a subordinate command, succeeding IX Corps, as a subordinate command of USARJ at Camp Zama on 1 November 1994. USARJ by that point was comprised of a headquarters at Camp Zama, Japan, supported by 19 assigned units, including the 9th Theater Support Command and a host of attached and tenant units and activities. The 10th and 17th Area Support Commands were eventually realigned to become part of the 9th Theater Support Command.

Also attached to USARJ was the US Army Corps of Engineers - Japan Engineer District (USACE-JED), one of 41 districts within the US Army Corps of Engineers. JED differed from stateside districts in 2 respects: First, it did not have a "civil works" mission, that is to say it had no congressionally-funded projects and programs such as flood control, dredging, hydroelectric power, and wetlands regulation. Second, much of JED's engineering and construction program was funded by the Government of Japan, through the bilateral Facilities Improvement Program (FIP). The Japan-funded FIP was a $1 billion a year program that was part of the way the Japanese government shared the burden of stationing US Forces in Japan. The program was supported by the US Congress through the annual expenditure of approximately $16 million of planning and design funds yielding a return of 50-60:1 for every US taxpayer dollar invested. The FIP program, implemented in 1979, built both operational and quality of life facilities in support of US Forces.

USARJ was in Japan to support the mutual defense of Japan, where it also provided a forward presence, bilateral engagement with Japan, and support for regional contingencies. All of the USARJ staff was assigned to and served in Japan. The same Commanding General led both USARJ and the 9th Theater Support Command, providing a unity of command and focus for US Army activities in Japan.

USARJ commanded all US Army units assigned or attached and employed them to conduct operations as directed by Headquarters, USFJ, and USARPAC. It planned and trained with the Japan Ground Self-Defense Force (JGSDF) for the defense of Japan, and supported regional contingencies by maintaining war reserve and operational project stocks. USARJ maintained storage facilities with the capability to expand the Asia logistical base, and provided humanitarian and disaster relief assistance to the region as requested. It provided garrison-type support in Japan, theater-wide support, and support for other commands as directed. USARJ developed, coordinated and prepared bilateral, and unilateral contingency plans for its areas of operation.

USARJ/9th Theater Support Command was committed to the support of the Treaty of Mutual Cooperation and Security between the United States and actively promoted coordinated operations between the Japan Ground Self-Defense Force and US Army in emergency situations through bilateral planning and training. The training involved an annual bilateral command post exercise, 2 annual field training exercises, and numerous other bilateral events.

USARJ and 9th Theater Support Command conducted over 140 bilateral engagements every year and the list grew each year. The dynamic exercise program of USARJ and 9th Theater Support Command offered exercise participants a "one-of-a-kind" bilateral training experience. Three major bilateral training exercises were conducted each year: Yama Sukara, Orient Shield, and North Wind. These exercises sought to refine key interoperability issues between the US Army and the JGSDF. Each exercise provided an opportunity to exchange lessons in culture through the "Home Visit Program." At the beginning and end the of each exercise, approximately 450 soldiers visited a host Japanese family in the local area where the exercises were held.

The most important annual exercise, Yama Sakura, usually held at the beginning of the calendar year, was a command post exercise (CPX) designed to enhance bilateral contingency planning. As many as 1,100 US soldiers would take part in the exercise each year, including hundreds of Army Reserve and National Guard soldiers from more than 27 states. I Corps was a key player and participated as a fully operational Army Corps headquarters, with assigned units to exercise with the JGSDF. Computer technology played a key role in Yama Sakura. The exercise, as with most CPXs, used the Corps Battle Simulation (CBS) for tactical play. This system enhanced and "drove" the scenario. It tracked the results of the command and staff actions and decisions. CBS allowed USARJ and 9th Theater Support Command to link up with participants in various locations throughout the Pacific area of operations. CBS also allowed a link to the JGSDF participating units to show the same picture for all, making it truly a bilateral operation.

North Wind was USARJ's premier cold weather field training exercise (FTX). This exercise involved realistic tactical planning, maneuver and live-fire training in a bilateral field setting. US and Japanese infantry soldiers trained together in air assault operations, ground assaults, ski and snowshoe maneuvers, and live-fire exercises.

Orient Shield was the third bilateral field training exercise that provided realistic tactical planning, maneuver, and live-fire training in a challenging field environment. This exercise was normally held late in the fall each year. Typically, the key participants were afforded the rare opportunity to integrate their soldier skills, working shoulder to shoulder towards a common training goal.

USARJ and 9th Theater Support Command also provided the life support for regional exercises such as Balikatan in the Philippines and Cobra Gold in Thailand. These exercises provided training opportunities to practice contingency deployment, force protection and logistical support mission over extended distances. USARJ and 9th Theater Support Command also participate in Ulchi Focus Lens, an exercise in Korea, as well as Receiving, Staging, Onward Movement and Integration exercises both in Korea and Japan. These exercises required performing the mission of a supporting theater support command, augmenting the Eighth US Army and 19th Theater Support Command, both in Korea.

In 2007, a forward element of I Corps, I Corps (Forward) was activated at Camp Zama in Japan. This element was merged with USARJ, which became USARJ/I Corps (Forward). At the time of its activation, I Corps (Forward) was expected to be operational by late 2009. The activation of I Corps (Forward) was part of a larger realignment of US Army forces in the Pacific region. As a result, the functions of the 9th Theater Support Command were subsumed by the new element and the 9th Theater Support Command was inactivated.

On 17 October 2012, it was reported that 58th Signal Battalion had been inactivated at Fort Buckner, Okinawa as part of a consolidation of signal assets in Japan.