The P-51D introduced the bubble canopy to improve rear visibility, with the fuselage redesigned starting from the tenth P-51B production airframe. The wing was modified with an added fairing over the undercarriage, creating the type's characteristic leading-edge 'kink'. Powered by the Packard V-1650-7 (a licence-built version of the Rolls-Royce Merlin 66), it became the definitive long-range escort fighter for the Eighth Air Force over Germany from mid-1944. 8,200 were built across the Inglewood, California and Dallas, Texas plants; 100 were shipped unassembled to Australia and 282 went to the RAF under Lend-Lease as the 'Mustang IV'.