Army cooperation planes combined the roles of artillery spotter aircraft, liaison, reconnaissance plane and close air support.
The concept of army cooperation units was invented in France at the end of World War I.
However, in most cases the roles of observation, reconnaissance and liaison were kept separate, with each assigned to a more specialised unit.
Typical Polish army cooperation planes included Lublin R-XIII, PZL Ł.2 and RWD-14 Czapla.
According to Polish specifications of the late 1920s, the army cooperation aircraft were capable of STOL, had folding wings and relatively small dimensions to allow them to operate from improvised airfields and improvised hangars such as barns.