Me 262 pilots claimed a total of 542 Allied aircraft shot down, although higher claims are sometimes made. The Allies countered its effectiveness in the air by attacking the aircraft on the ground and during takeoff and landing. Strategic materials shortages and design compromises on the Junkers Jumo 004 axial-flow turbojet engines led to reliability problems. Attacks by Allied forces on fuel supplies during the deteriorating late-war situation also reduced the effectiveness of the aircraft as a fighting force. Armament production within Germany was focused on more easily manufactured aircraft. In the end, the Me 262 had a negligible impact on the course of the war as a result of its late introduction and the consequently small numbers put in operational service.