04/30/2019. Remarks by Jack McKillop: "On May 12, 1931, the USAAC ordered 30 O-25Cs. This version of the O-25 had a Preston-cooled geared Curtiss V-1570-27 twelve-cylinder, two bank, liquid-cooled engine in a streamlined cowling. The radiator had been moved further aft and a spinner was fitted over the propeller.

This was the last Douglas observation biplane equipped with a liquid-cooled engine."