This paper addresses the US Forces and Military Bases in Japan from 1945 to 1960 focusing on the impacts by the Korean War. The outbreak of the war, triggering the Peace Treaty and the Japan-US Security Treaty, had fundamentally redefined the strength of the US Forces and deployment in Japan. The Japan-US Security Treaty singed in 1951 had changed the US Occupation Forces into the deployed ones commissioned for keeping military balance in the East Asia and Deterring War. This paper studies on the characteristics of the US Forces in Japan transforming from the occupation forces, the UN Forces waging the war, to readiness-forces, and development of the Military Bases with three periods of occupation, transient and initial alliance periods. It assumes the close correlation of the US Government Policies reflecting of the 'Defensive Perimeter' announced by Dean Acheson, Secretary of the States Affairs in January 1950, the US National Security Counsel documents and so on.
The paper argues that the outbreak of the war had been so critical in terms of the US Security Policy of Political Containment that the US Forces and Military Bases in Japan were totally redefined militarily to contain the growth of communism and seek for deterring another war in the Korean Peninsula as well as in the Asian Theater. Referring to the Japan-US Security issued in 1951, the US Commitment to prevent the war including Japan's Security Policy as the US Partner has been reflected on the Strength of the US Forces and Deployment of Military Bases in Japan. And it goes without saying that Japan has continuously supported the US Commitment. The Fundamental Military Framework in the East Asia has been formed by the outbreak of the Korean War and presently still remains irrespective of the End of Cold War.