On 1 July 1920, he was commissioned a second lieutenant in the Regular Army Air Service, and the following month returned to Mather Field for duty with the 91st Squadron as radio officer.

Entering the Air Corps Tactical School at Maxwell Field, Alabama, in August 1932, Gardner graduated the following June and remained there as an instructor.

In April 1935 he went to Rockwell Field for special training in navigation and instrument flying and then resumed his former duties at Maxwell that July.

That October he returned to Wright Field as chief of the Armament Laboratory in the Air Corps Material Division; served as military air observer in London, England, from April to June 1940; and then returned to Wright Field as assistant technical executive in charge of armament in the Materiel Division.

Col. Gardner, the press made no mention of his recent (March 1942), and still secret, training at Eglin for the Doolittle Raid.

[2] By late 1943, Maj. Gen. Henry H. Arnold directed Gardner's electronic engineers at Eglin Field, Florida, to outfit war-weary bombers with automatic pilots so that they could be remotely controlled.

On 3 October, he was appointed a special assistant to the secretary of the Air Force, and in September 1948 was named director of installations.

17 (1946),[14] the Legion of Merit with Oak Leaf Cluster, and Honorary Commander of the Military Division of the Most Excellent Order of the British Empire.