 After graduation, from 1938 to 1940, he worked as an accountant for the Tennessee Valley Authority, where Kohler had become Controller.There, he worked on performance auditing and the mathematical allocation of resources, and helped Kohler testify to a congressional investigative committee.In 1940, Cooper started doing graduate studies at Columbia University; however, in 1942, with his coursework completed but his thesis unwritten, he left Columbia to serve his country during World War II.