On May 8, 1942, the USAAF awarded Lockheed a contract (AC22346) for 300 advanced trainers. They were assigned the designation AT-18.
The AT-18-LO version was constructed as a gunnery trainer. It was powered by a pair of 1200-hp Wright R-1820-87 engines. The AT-18 was equipped with a Martin dorsal turret containing a pair of 0.50-inch machine guns. This turret was standard on most US wartime bombers. 217 AT-18s were built.
The AT-18A-LO version was an unarmed navigational trainer, with accommodation for pilot, instructor, and three students. 83 were built. It was also powered by the R-1820-87 engine.
AT-18A-LO USAAF 42-55485/55567 AT-18-LO USAAF 42-55568/55784