The USAAF contracted with new manufacturer Interstate for 250 of their S-1B tandem seat liaison aircraft designating it as L-6 but overheating problems with its 115hp Franklin engine were never fully solved. This one was registered N60458 postwar

When the US entered WWII, the USAAF contracted with Interstate for 250 S-1B aircraft, designating the prototype as the XO-63. It was the last aeroplane to use the 'O' (for observation) designation, later the production planes were re-designated L-6s. However, the aircraft had significant overheating problems that were only partially solved and had the dubious distinction that fewer L-6s were built than any other USAAF liaison/utility aircraft. This example is on display at the National Museum of the USAF.