Complex sentence: Roosevelt appointed Hillman to the National Defense Advisory Committee in 1940 and named him associate director of the Office of Production Management in 1941; when FDR created the War Production Board in 1942, he appointed Hillman to serve as the head of its labor division.
Split into simpler sentences: Roosevelt appointed Hillman to the National Defense Advisory Committee in 1940 and named him associate director of the Office of Production Management in 1941. When FDR created the War Production Board in 1942, he appointed Hillman to serve as the head of its labor division.