Under the guidance of his new commander, who recognised the latent potential in the young officer, Marseille quickly developed his abilities as a fighter pilot. He reached the zenith of his fighter pilot career on 1 September 1942, when during the course of three combat sorties he claimed 17 enemy fighters shot down, earning him the "Ritterkreuz mit Eichenlaub, Schwertern und Brillanten" (Knight's Cross with Oak Leaves, Swords, and Diamonds). Only 29 days later, Marseille was killed in a flying accident, when he was forced to abandon his fighter due to engine failure. After he exited the smoke-filled cockpit, Marseille's chest struck the vertical stabiliser of his aircraft. The blow either killed him instantly or incapacitated him so that he was unable to open his parachute.