 In July 1936 he was sent to the Odessa Military Aviation School of Pilots to attend combat courses, and after completing them he worked as a flight instructor for pilots who were going to be deployed to Spain.From June to October 1938 Gritsevets was deployed in Spain as the commander of the 5th Free-hunting Squadron as part of the Soviet Union's assistance to the Spanish Republican Air Force.Throughout the conflict he gained 115 flight hours in combat, flew 88 combat sorties, engaged in 42 dogfights, gained eleven shared victories, and at least one solo victory; sources widely differ about the number of victories he gained in Spain.