High command
Following the United States entry into World War II, Harrison was promoted to the temporary rank of Colonel on December 11, 1941, just four days after Japanese attack on Pearl Harbor. He was appointed Deputy Chief of Strategy &amp; Policy Group, War Plans Division, War Department General Staff and also was given additional duty at General George C. Marshall's Committee on Allocation of Responsibilities which was given the job of figuring out a reorganization of the Army High command. For his service in this capacity, Harrison was promoted to the temporary rank of Brigadier general on June 26, 1942.