From Wiki:
The Mustang was designed to use the Allison V-1710 engine, which had limited high-altitude performance in its earlier variants. The aircraft was first flown operationally by the Royal Air Force (RAF) as a tactical-reconnaissance aircraft and fighter-bomber (Mustang Mk I). Replacing the Allison with a Rolls-Royce Merlin resulted in the P-51B/C (Mustang Mk III) model and transformed the aircraft’s performance at altitudes above 15,000 ft (4,600 m) (without sacrificing range),[9] allowing it to compete with the Luftwaffe’s fighters.[10] The definitive version, the P-51D, was powered by the Packard V-1650-7, a license-built version of the two-speed two-stage-supercharged Merlin 66, and was armed with six .50 caliber (12.7 mm) AN/M2 Browning machine guns.[11]
re: tag line
I have a coffee cup that reads:
Trust your mother but cut the cards...
I thought about specifying the p51D immediately after I posted. I remembered there were several variants, but in my def need, P51D is the one we most often see in movies, documentaries, etc