Though not officially a belligerent during the Korean War (1950–1953), the Soviet Union played a significant, covert role in the conflict. It provided material and medical services, as well as Soviet pilots and aircraft, most notably MiG-15 fighter jets, to aid the North Korean-Chinese forces against the United Nations Forces. Joseph Stalin had final decision-making power and several times demanded North Korea postpone action, until he and Mao Zedong both gave their final approval in spring 1950.