USARJ maintains and strengthens the credibility of deterrent power in the Pacific through maintenance of defense facilities, war reserves and operational project stocks.

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 (Forward) is responsible for providing support of Article V (Defense of Japan) and VI (ensuring regional stability) of the U.S.-Japan Mutual Security Treaty.

Reorganized in September 1968, USARJ employed a new structure to maximize operational efficiency, while keeping its existing missions and functions.

There were several minor reorganizations and redesignations over the next decade, so that by September 2001, USARJ consisted of logistics bases in Japan and Okinawa.

In December 2007, I Corps (Forward) was activated in Japan in line with the Army's transformation efforts.

USARJ remains headquartered at Camp Zama, where it engages in numerous bilateral activities with the Japan Ground Self-Defense Force (JGSDF), and performs duties as United States Forces Japan's Army Component Command.