Complex sentence: In April 1951 he returned to Tactical Air Command and was promoted to lieutenant general, and in June went back to Tokyo as commanding general of Far Eastern Air Forces and the United Nations Air Forces when Lieutenant General George Stratemeyer had a heart attack.
Split into simpler sentences: In April 1951 he returned to Tactical Air Command and was promoted to lieutenant general. In June 1951 he went back to Tokyo as commanding general of Far Eastern Air Forces and the United Nations Air Forces when Lieutenant General George Stratemeyer had a heart attack.