日本国とアメリカ合衆国との間の相互協力及び安全保障条約
Under the terms of the Treaty of Mutual Cooperation and Security between the United States and Japan, United States forces stationed in Japan were to deal with external aggression against Japan while Japanese forces, both ground and maritime, would deal with internal threats and natural disasters. Only after the outbreak of the Korean War did MacArthur authorise Prime Minister Shigeru Yoshida to establish a 75,000 strong National Police Reserve. The next expansion came in 1952, when as a compromise in the face of U.S. calls to build up an army of 350,000, the National Police Reserve was re-titled the National Safety Force and expanded to 110,000.