[1] The United States Army Air Corps (USAAC) issued a specification for a specialized bomber trainer, ordering two prototypes from Fairchild Aircraft.

[2] The concept was to have a single type that was able to duplicate the bomber crew positions from piloting, navigation, bomb aiming/dropping to aerial gunnery.

[5] The AT-21 proved unsuitable for use as a trainer due to vibration and oscillation tendencies, as well as an inherent instability caused by the short distance between the rudders and the gull wing.

[7] A small number of AT-21s survived as civilian examples, with one (s/n 42-48053 owned by Craig Cantwell) still in existence in North Texas awaiting restoration.

Optionally piloted for flight testing and intended to carry 4,000 lb (1,800 kg) of explosive, the XBQ-3 first flew in July 1944, but the project was cancelled later that year.