Meanwhile, the Luftwaffe continued to defend German-occupied Europe against the growing offensive power of RAF Bomber Command and, starting in the summer of 1942, the steadily building strength of the United States Army Air Forces. The mounting demands of the Defence of the Reich campaign gradually destroyed the Luftwaffe's fighter arm. Despite its belated use of advanced turbojet and rocket propelled aircraft for bomber destroyer duties, it was overwhelmed by Allied numbers and a lack of trained pilots and fuel.