The Interstate Company entered the aircraft-manufacturing field in 1940 with the S-1A "Cadet," a tandem seat liaison airplane. When the United States entered World War II the U.S. Army Air Forces (AAF) contracted with Interstate for 250 S-1A aircraft, designating the prototype as the XO-63. It was the last airplane to use the "O" as the observation designation.
Later, the AAF designated the production airplane as the L-8. The aircraft, however, had significant overheating problems that were only partially solved. It had the dubious distinction that fewer L-8s were built than any other AAF liaison aircraft. The AAF used the L-8 as a utility transport, liaison, and training aircraft in the United States, but never shipped it overseas. After the war the remaining L-8s were sold as surplus.