During 1919-1920 he served as assistant air officer for the Western Department; he reverted to captain in February 1920 and received promotion to permanent major in July. Spaatz served as commander of Mather Field, California, in 1920; as commander of Kelly Field, Texas, in 1920-1921; as air officer, VIII Corps, in 1921; as commander of the 1st Pursuit Group of Selfridge Field, Michigan, in 1922-1924; in the office of the chief of the Air Corps in 1925-29; as commander of the 7th Bombardment Group at Rockwell field, California, and subsequently of Rockwell Field in 1929-1931; and as commander of the 1st Bombardment Wing at March Field, California, in 1931-1933.
During January 1-7, 1929, Spaatz and Captain Ira C. Eaker, along with Sgt. Roy Hooe and others, established a flight endurance record of 150 hours, 40 minutes, in a Fokker aircraft, the Question Mark, over Los Angeles. After two years as chief of the training and operations division in the office of the chief of Air Corps and promotion to lieutenant colonel in September 1935, he entered the Command and General Staff School, Fort Leavenworth, Kansas, graduating in 1936. He was executive officer of the 2nd Wing at Langley Field, Virginia, until 1939 and then again joined the staff of the chief of the Air Corps. After a tour of observation in England in 1940 he was promoted to temporary brigadier general and named to head the material division of the Air Corps, and in July 1941 he became chief of the air staff under General Henry H. “Hap” Arnold, chief of the (renamed) Army Air Force.
In January 1941 he was appointed chief of the Air Force Combat Command. Later in that year he returned to England to begin planning the American air effort in Europe. In May he became commander of the Eighth Air Force, and in July he was designated commander of U.S. Army Air Forces in Europe. In November he went to North Africa to reorganize the Allied air forces there for General Dwight D. Eisenhower, becoming commander of the Allied Northwest African Air Forces (NWAAF) in February 1943. In march he was promoted to temporary lieutenant general. from March to December 1943 he was also commander of the Twelfth Air Force, a unit of the NWAAF, which took part in both the North Africa and Sicily campaigns. In January 1944 Spaatz was named commander of the Strategic Air Force in Europe; his command included the Eighth Air Force under General James H. “Jimmy” Doolittle, based in England, and the Fifteenth Air Force under General Nathan F. Twining, based in Italy, and had responsibility for all deep bombing missions against the German homeland. In March 1945 he was promoted to temporary general, and in July, war in Europe having ended, he took command of Strategic Air Force in the Pacific. The atomic bombing of Hiroshima and Nagasaki took place under his command.
In March 1946 he succeeded General Arnold as commander in chief of the Army Air Forces, and he became the first chief of staff of the independent air force in September 1947. He held that post until retiring in July 1948 in the rank of general. He served subsequently as chairman of the Civil Air Patrol and for a time contributed a column to Newsweek magazine. Spaatz died in Washington, D.C., on July 14, 1974 and was interred on the grounds of the U.S. Air Force Academy.