[62] He became a lieutenant colonel in 1925 and a colonel in 1932.[63] In the 1920s and 1930s he commanded 1st Battalion, 379th Field Artillery, 102d Infantry Division.[64] After promotion to colonel, Truman advanced to command of the same regiment.[65]
After his election to the U.S. Senate, Truman was transferred to the General Assignments Group, a holding unit for less active officers, although he had not been consulted in advance.[66] Truman protested his reassignment, which led to his resumption of regimental command.[66] He remained an active reservist until the early 1940s.[67] Truman volunteered for active military service during World War II, but was not accepted, partly because of age, and partly because President Franklin D. Roosevelt desired senators and congressmen who belonged to the military reserves to support the war effort by remaining in Congress, or by ending their active duty service and resuming their congressional seats.[68] He was an inactive reservist from the early 1940s until retiring as a colonel in the then redesignated U.S. Army Reserve on January 20, 1953.