Prior to World War II, Richardson commanded the 1st Cavalry Division from 1940-1941. He then directed the War Department Bureau of Public Relations before becoming Commanding General of the VII Corps in Alabama, moving it to set up the defense of California immediately following the bombing of Pearl Harbor. In 1943 he was made Commanding General of the Hawaiian Department, Military Governor of Hawaii, and all Army personnel in the Pacific Ocean and Mid-Pacific Areas. As Commander of all Pacific Army personnel, he had administrative or what is called UCMJ authority of all Army units, while tactical or what is called today operational Joint control fell to Fleet Admiral Chester W. Nimitz. He was responsible for all Army disciplinary, training, and tactical unit preparations. He was the first senior Army general officer to ever serve as Joint forces subordinate commander under a non-Army flag officer, Fleet Admiral Nimitz.