Arado AR68

The Arado Ar 68 was a German single-seat biplane fighter used by the Luftwaffe from 1936 to 1940, with limited combat in the Spanish Civil War (1938) and as a night fighter during the early, initial phase of World War II. It served as a stopgap fighter before being replaced by the Messerschmitt Bf 109 and was later used for advanced training until 1944. 
 
Key Usage and Deployment:
Luftwaffe (Germany): Entered service in early 1936, with early units stationed in East Prussia and involved in the 1936 Remilitarization of the Rhineland.
Spanish Civil War: Deployed with the Condor Legion in 1938, where it was considered outclassed by the Soviet Polikarpov I-16.
Early World War II: Served as an interim night fighter, notably with 10. and 11. (Nachtjagd)/JG 72 and 10. (Nachtjagd)/JG 53, through the winter of 1939–1940.