Large numbers of Lockheed B14L Hudson aircraft were supplied to the RAF to act as light bombers and maritime patrol aircraft. Under Lend-Lease arrangements they were designated A-28 and A-29, and the USAAF repossessed several of the latter for its own use. The AT-18 was developed from the A-29 to satisfy USAAF needs for training.

Essentially similar to the A-29, the AT-18 featured a Martin dorsal turret with twin 50-caliber machine guns. This turret was in widespread use on US bombers, and the AT-18 provided training for gunners. Later this variant was employed as a target tug. Procurement totaled 217 (serialled 42-55568/42-55784), and was followed by 83 unarmed and turretless AT-18As (42-55485/42-55567) which were used in the navigation training role.