Complex sentence: He became Chief of Staff of the Fifth Air Force in September 1942, before returning to the United States in 1944 to become Assistant Chief of Staff, United States Army Air Forces for Organization, Commitments and Requirements.
Split into simpler sentences: He became Chief of Staff of the Fifth Air Force in September 1942. He returned to the United States in 1944 to become Assistant Chief of Staff, United States Army Air Forces for Organization, Commitments and Requirements.