This apparent lack of success is accounted for in several ways. The German industrial economy was so strong, its industrial bases so widely spread, that it was a hopeless task to try and crush it by area bombing. Further, up until 1943 it is undoubtedly the case that Germany was not fully mobilised for war, Speer remarked that single shift factory working was commonplace, and so there was plenty of slack in the system. It has been argued that the RAF campaign placed a limit on German arms production. This may be true but it is also the case that the German forces did not run out of arms and ammunition and that it was manpower that was a key limiting factor, as well as the destruction of transport facilities and the fuel to move.