Considered by many to be one of the, if not the, most produced aircraft of all time, with estimates of aircraft completed ranging from 30,000 to 40,000, the Polikarpov PO-2, also known as the U-2, primary trainer biplane flew for the first time on 7 January 1928.

The Stampe series of tandem two-seat primary training biplanes was designed by Count Stampe in Belgium, and manufactured by the Stampe-et-Vertongen concern in Belgium.