Robert Ellingson arrived in Oak Ridge in June 1943. Shortly after Ellingson arrived, however, he was informed by his employer, Tennessee Eastman, that they already had too many chemists and chemical engineers. Instead of them away, however, Ellingson and the others in his group were sent to the University of California, Berkeley for the summer to learn how to operate the machinery at Oak Ridge.
That fall, Ellingson returned to Oak Ridge and began work as a technical supervisor in the Refining Division at the Y-12 separations facility. Ellingson worked closely with the operational formeman to ensure that all units in the process were operating correctly.
After the war, Ellingson remained in Oak Ridge and married his wife, Evelyn. He continued to work at Y-12 for several years after the war and later transferred to the chemical building, where he worked until he retired.