One Douglas O-2, serial number25-380, was modified for the new role as an attack aircraft, while the basic structure of the aircraft remained, there were several modifications made. The water-cooledLiberty engine (V-1650) of the O-2 was replaced by an inverted air-cooled Allison VG-1410 engine. The reason for this was that water cooling system was seen as too vulnerable to enemy attack. The lower engine cowlings were omitted to allow for more cooling air flow over the engine. Second, the A-2 was more heavily armed than the O-2. The A-2 had six forward-firing .30-caliberBrowning machine guns - two in the nose forward of the cockpit, and two each in the mid-upper and lower wings. Two .30-caliber Lewis guns were put on a flexible mount for use by the observer-gunner in rear defense of the aircraft. The aircraft also had the capacity for a small bomb load of 100 lb (45 kg).
The Douglas XA-2 was evaluated against the Curtiss XA-3 (a conversion of the Curtiss O-1B observation plane). The Douglas aircraft won the initial competition, but the Army realized that the Liberty engine was both under-powered and in dwindling supply. It ordered a second competition with both models upgraded with Packard 1A-1500 engines. The Curtiss aircraft won this time and became the U.S. Army Air Corps' front-line attack aircraft (Curtiss A-3 Attack Falcon) from 1928 to 1935.