Complex sentence: He was appointed Chairman of the National Defense Research Committee in 1940 by President Franklin D. Roosevelt, appointed Director of the Office of Scientific Research and Development in 1941, and from 1946 to 1947, he served as chairman of the Joint Research and Development Board.
Split into simpler sentences: He was appointed Chairman of the National Defense Research Committee in 1940 by President Franklin D. Roosevelt. From 1946 to 1947, he served as the chairman of the Joint Research and Development Board.