The Bf 109 was the backbone of the Luftwaffe fighter force in World War II, although it began to be partially replaced by the Focke-Wulf Fw 190 from 1941. The Bf 109 scored more aircraft kills in World War II than any other aircraft. At various times it served as an air superiority fighter, a bomber escort, an interceptor, a ground-attack aircraft, and a reconnaissance aircraft. Although the Bf 109 had weaknesses, including a short range, and especially a sometimes difficult to handle narrow, outward-retracting undercarriage, it stayed competitive with Allied fighter aircraft until the end of the war.