After serving a stint at the Aberdeen Proving Ground during World War II, he joined the staff of the National Bureau of Standards (NBS, now the National Institute of Standards and Technology), where he was hired as the first theoretical physicist on the NBS staff. He served there until 1966, when he joined the faculty of physics at the University of Chicago. There he trained, until the early 1990s, about thirty graduate students and postdoctoral research associates, many of whom now occupy leading positions in theoretical atomic and molecular physics in the United States, Europe, and Japan.