Ronald Reagan enrolled in a series of home-study Army Extension Courses on March 18, 1935. After completing 14 of the courses, he enlisted in the Army Enlisted Reserve on April 29, 1937, as a Private assigned to Troop B, 322nd Cavalry at Des Moines, Iowa. He was appointed Second Lieutenant in the Officers Reserve Corps of the Cavalry on May 25, 1937.  On June 18, 1937 Reagan, who had just moved to Los Angeles to begin his film career, accepted his Officer's Commission and was assigned to the 323rd Cavalry.

Lieutenant Reagan was ordered to active duty on April 19, 1942. Due to his poor eyesight, he was classified for limited service only excluding him from serving overseas. His first assignment was at the San Francisco Port of Embarkation at Fort Mason, California, as liaison officer of the Port and Transportation Office. Upon the request of the Army Air Forces (AAF), he applied for a transfer from the Cavalry to the AAF on May 15, 1942; the transfer was approved on June 9, 1942. He was assigned to AAF Public Relations and subsequently to the 1st Motion Picture Unit in Culver City, California. Reagan was promoted to First Lieutenant on January 14, 1943 and was sent to the Provisional Task Force Show Unit of This Is The Army at Burbank, California. Following this duty, he returned to the 1st Motion Picture Unit, and on July 22, 1943 was promoted to Captain.

In January 1944, Captain Reagan was ordered to temporary duty in New York City to participate in the opening of the sixth War Loan Drive. He was assigned to the 18th AAF Base Unit, Culver City, California on November 14, 1944, where he remained until the end of the war. He was recommended for promotion to Major on February 2, 1945, but this recommendation was disapproved on July 17, 1945. On September 8, 1945, he was ordered to report to Fort MacArthur, California, where he was separated from active duty on December 9, 1945.

While on active duty with the 1st Motion Picture Unit and the 18th Army Air Forces Base Unit, Captain Reagan served as Personnel Officer, Post Adjutant, and Executive Officer. By the end of the war, his units had produced some 400 training films for the Army Air Forces.

Reagan's Reserve Commission automatically terminated on April 1, 1953. However, he became Commander-in-Chief of all U.S. Armed Forces when he became President on January 20, 1981.