For a short time, from January 6, 1937, Tinker served in a light bomber squadron, flying obsolete Breguet 19 bombers. From January 23, he, along with some other American pilots, was assigned to a fighter unit, 1st "Escuadrilla de Chatos" commanded by Andrés García La Calle, flying Soviet Polikarpov I-15 "Chato" biplanes. In 1937, he flew many combat missions against the Fascist Falange air forces, generally duelling Germans and Italians. The squadron first entered action on February 10, and took part in a Battle of Guadalajara. On March 14, Tinker shot down his first aircraft, an Italian Fiat CR.32 fighter, followed by another CR.32 on March 20. On April 17, he shot down a German Heinkel He 51 fighter from Legion Condor over Teruel.