The North American P-51 Mustang powered by the British-designed Rolls-Royce Merlin/Packard engine was, quite simply, the best long-range escort fighter of the World War Two era. Entering service in November 1943, it curtailed prohibitive losses suffered by the heavy bombers of the US Eight Army Air Force which carried out the strategic daylight bombing campaign against the Third Reich. In the European Theater of Operations the USAAF also deployed Mustangs, with great success, as free-ranging strafers, fighter-bombers, scouts and reconnaissance aircraft. Eventually, it was the P-51 that broke the backbone of the Luftwaffe.