Curtiss A-3 (Model 44) was an attack version of the O-1 Falcon two-seat observation aircraft of the Army Air Service.

    In 1924 the Army scheduled a competition for a successor to the aging DH-4Bs and -4Ms still serving with the Air Service. Since the Army still had a large number of surplus Liberty engines left over from WW1, the War Department ordered that the competitors in the observation plane contest fit their first entries with this engine. The trials were to begin in November of 1924.

The Curtiss entry was the XO-1 [23-1252] powered by a water-cooled 420hp Liberty V-1650-1. It was a fairly conventional two-seat biplane with a single bay wing on N-type interplane struts. It had unique fuselage construction techniques for its tim—aluminum tubing bolted and riveted together with steel tie-rod bracing. The wings were wooden-framed with a wire trailing edge and the new Clark-Y aerofoil. The center section was well forward for pilot access and visibility, so the upper wing panels had to be swept back nine degrees to achieve balance.

    The Curtiss design took second place to Douglas XO-2 in the 1924 observation plane contest; however, the Army was fully aware that the supply of surplus Liberty engines would not last forever, nor would they be suitable much longer as a powerplant for future first-line military aircraft. Consequently, in 1925, another contest was held for observation types to be powered by the 510hp Packard 1A-1500, a more advanced V-12 liquid-cooled engine. Conversion of the XO-1 to the 1A-1500 was fairly straightforward. Then the Curtiss design won the contest, and an order for ten production aircraft was issued as O-1 [25-325/334].

Unfortunately, the Packard did not live up to expectations, so the ten O-1s differed from the prototype in having it replaced by the liquid-cooled 435hp Curtiss D-12 (V-1150), which was D-12 was less powerful than the Packard, so performance suffered. Additionally, tail surfaces had to be revised to increase fin area and decrease rudder area. Armament consisted of a single forward-firing .30 Browning machine gun in the engine cowling and a pair of .30 Lewis guns on a Scarff ring in the rear cockpit

    O-1B was the first major production variant, and included wheel brakes, a dropable 56-gallon belly tank, and provisions for dumping the fuel in the 113-gallon main fuel tank. 45 were ordered in 1927 [27-243/287].

A-3 was an attack version of O-1B, almost identical, but with minor changes of adding underwing bomb racks and a single .30 machine gun in each lower wing outboard of the propeller arc. 66 A-3s were ordered on three contracts [27-243/262, -298/317, 28-83/108]. The first A-3 was ready by Oct 31, 1927. Six were fitted with dual controls for the training of observers and redesignated as A-3A [27-306, 27-310, 27-315, 28-116/118].

    A-3B (Model 37H) in 1929 was an attack version of the later O-1E. O-1E was an improved -1B with the V-1150-5 and refinements of engine cowling lines, balanced (Frise) ailerons, horn-balanced elevators, oleo-pneumatic shock absorbers, E-4 gun synchronizer system, and a 36-gallon belly tank. 78 attack equivalents of O-1E were ordered under the designation A-3B in two separate contracts [30-1/28, -231/280]. The first was tested in Apr 1930. [30-1] was converted to O-1E configuration. The last A-3B in service was scrapped in Oct 1937 [30-13].

Attack Falcons equipped all four of the Air Corps' ground attack units—8th, 13th, and 19th Squadrons of 3rd Attack Group at Fort Crockett TX, and 26th Attack Squadron based in Hawaii.