By September 1, 1951, the Communists had 525 MiGs in action against only 105 USAF F-86s. The enemy decided to overwhelm U.N. air forces to gain aerial superiority and began concentrating on destroying USAF F-84 fighter-bombers flying at low altitudes. The USAF then doubled its F-86 force in order to have sufficient "Sabres" for both escorting friendly airplanes and for intercepting enemy planes. USAF combat results rapidly improved.