The first production version of the Mustang to be equipped with the Merlin engine was the P-51B. Identical airframes were produced at North American's Dallas plant and were designated P-51Cs. By the time these variants were ordered, America was in a full wartime economy, and production numbers of these Mustangs were in the thousands instead of the hundreds. The British received these two variants as well and named them Mustang Ills. Seventy-one P-51Bs and twenty P-51Cs were fitted with cameras and designated F-6Cs.
By mid-1944, P-51 Mustangs were fast replacing other types of fighters in the USAAF. The early variants with Allison powerplants were combat veterans and had proven to be superior in performance over any other allied fighter below 15,000 feet. The Merlin-powered P-51B and P-51C possessed outstanding high-altitude performance that made them formidable adversaries to any enemy aircraft above 12,000 feet. Additionally, all Mustang variants had great range capabilities which exceeded most other fighter aircraft of World War II.
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