07/31/2011. The seventh of the ten O-1 Observation Type aircraft (ordered by the USAAS under the s/n 25-325 to 25-334) was returned to Curtiss for a change to the new 600 hp Curtiss V -1570 Conqueror engine uprated to 730 hp at 2,600 rpm as one of the Army's entries in the Liberty Engine Builders Trophy event of the 1927 National Air Races.

Additionally, both wings were modified to accommodate surface radiators in the old PW-8 style as a drag-reduction measure. Best straightaway speed was 176.5 mph (284 kmh) and speed round a closed course to win the Liberty Engine Builders Trophy was 170.5 mph (274.38 kmh). The sole XO-13A was scrapped in 1930 with 482 flying hours. View also photo 10766.