The German and Italian air forces sent 'volunteer' units to Spain in the form of the Legion Condor and Aviazione Legionaria respectively, participating directly in the fighting. German and Italian aircraft were also supplied to the Spanish Nationalist Air Force, allowing it to expand from a couple of dozen obsolescent types in 1936 to a considerable force in 1939: five Grupo of fighters, 13 of multi-engine bombers and seven of light bombers/attack aircraft.

By and large the German and Italian pilots of the Legion Condor and Aviazione Legionaria flew the most modern aircraft, passing on older types to the Nationalist Air Force. For example the standard German fighter at first was the Heinkel He 51 biplane, as these were replaced in the Legion Condor with Messerschmitt Bf 109s from 1937, the He 51s were transferred to the Nationalists. Four of the five fighter Grupo in 1939 were still equipped with He 51 and CR.32 biplanes, but one had monoplane He 112 and Bf 109 supplied by Germany.

(From The Spanish Civil War - Nationalist Forces, Alejandro de Quesada)