09/30/2014. The sole AT-3 was the next to last aeroplane of the PW-9A order converted to an experimental single-seat advanced trainer by substitution of a 180 hp war-surplus Wright-Hispano Model E engine for the 435 hp Curtiss D-12. This change was made at the request of the Army and was duplicated by Curtiss when the same type of engine was installed in a Curtiss P-1A fighter airframe, creating the AT-4.
The resulting trainers were considerably lighter than the fighters and, with less than half the horsepower, were considerably slower. The high speed of some 129 mph (208 kmh) for the AT-3 does not compare favorably with WW I fighters powered with the same engine until allowance is made for the greater size of an aeroplane designed to carry a 435 hp engine and the use of a structure designed to military load factors at that power and weight. Since the structural elements of the AT-3 and AT-4 were not reduced in proportion to the power, the trainers were neither as fast nor as maneuverable as they could have been if designed for the purpose. The general unsuitability of the conversion is reflected by the fact that most of the 35 production AT -4s ordered from Curtiss were soon converted to P-1Ds by installation of D-12 engines.