A liaison aircraft (also called an
army cooperation aircraft) is a small, usually unarmed
aircraft primarily used by military forces for artillery observation or transporting commanders and messages. The concept developed before
World War II and included also battlefield
reconnaissance,
air ambulance, column control, light cargo delivery and similar duties. Able to operate from small, unimproved fields under primitive conditions, with
STOL capabilities, most liaison aircraft were developed from, or were later used as
general aviation aircraft. Both fixed-wing aircraft and
helicopters can perform liaison duties.