Curtiss O-52 Owl.

 A U.S. Air Force Curtiss O-52 Owl at the National Museum of the United States Air Force, Dayton, Ohio (USA). In 1940 the U.S. Army Air Corps ordered 203 Curtiss O-52s for observation duties -- signified by the designation "O" -- and used them for military maneuvers within the continental United States. Upon America's entry into World War II, however, the U.S. Army Air Forces realized that the airplane lacked the performance necessary for combat operations overseas. As a result, the Army relegated the O-52 to stateside courier duties and short-range submarine patrols off the coasts of the United States. The O-52 was the last "O" type airplane procured in quantity for the Army. Following the attack on Pearl Harbor, the Army Air Forces cancelled the "O" designation and adopted "L" for the liaison type airplanes that replaced it.