Several German military aircraft were brought from Spain for examination. Some were so badly damaged that they had to be examined on the ground, while others were restored and test flown. They even took part in simulated air combat with Soviet fighters. In 1937-1938, Air Forces Scientific Research Institute specialists familiarized themselves with He 51 and Bf 109 (with Jumo 210 engine) fighters, as well as Ju 52, Ju 86, and He 111 bombers.
In general, the results of testing gave some hope: the flight characteristics of the Soviet aircraft exceeded -those of German planes. As proof, I will provide a few excerpts from Scientific Research Institute reports on the results of the simulated air combat.
1. He 51 fighter (designated 1-25, flown by Stefanovskiy in 1938 in the USSR): Despite its low speed (315 km/h), the 1-25 can engage in active defensive combat against 1-16, M25, DI-6, and DI-6Sh airplanes and be successful in a surprise attack on SB, DB-3, and R-9 planes, but it cannot retain the combat initiative. In combat against the 1-16, the latter has all the advantages".