[1] He joined the United States Army as a member of the Coast Artillery Corps on August 20, 1910, and quickly transferred to the Infantry Branch.

[5] Shortly after the American entry into World War I, in April 1917, Landrum was assigned to the 43rd Infantry Regiment, and performed duty as aide-de-camp to Robert K. Evans in the Philippines.

[7] After the war Landrum continued his army career, receiving promotion to captain and carrying out Infantry and Adjutant General assignments in Washington, D.C., and at forts including Leavenworth, Benning, and Lewis.

[12][13] When the United States entered World War II in December 1941 Landrum was Chief of Staff of the 3rd Infantry Division at Fort Lewis, after receiving a temporary promotion to colonel in June 26.

[19][20][21] Landrum was promoted to temporary major general on March 13, 1943[13] and commanded the 87th Infantry Division during its training in the United States.

[23] Major General J. Lawton Collins, commanding the VII Corps, became concerned that the 90th, which had not seen service in the war so far, was not performing effectively in combat.

[27] Upon returning to the United States Landrum succeeded Robert L. Spragins as commander of the 71st Infantry Division during its mobilization and training before it departed for combat in Europe.

[30] Following World War II Landrum returned to his permanent rank of colonel and continued his career, including assignment as Deputy Chief of Staff of the Fifth Army in Chicago.

[38] He died in Springfield, Illinois, on July 24, 1967, and was buried at San Francisco National Cemetery, Section DE, Site 17-A.