The P-51A used the V-1710-81 with 1,360-hp war emergency boost, and first flew February 3, 1943. By May 1943, 310 were delivered before production shifted to the P-51B. Armed with four .50-caliber wing guns with 1,260 rounds, and wing racks for two 500-pound bombs or two 75-gallon drop tanks, or fitted with two 150-gallon ferry tanks, the
P-51A was judged to have “the best all-around fighting qualities of any present American fighter” below 22,000’.
While serving the 1st Air Commando group in Burma, the P-51A became the first AAF fighter to fire rockets in combat. Three “bazooka” tubes installed under each wing launched 4.5-inch rockets at a Japanese air base on April 4, 1944.
Mustangs with Merlins
In the United States, the Air Force authorized a parallel Merlin project on June 12, 1942, and North American submitted the NA-101 specification July 24. A contract was issued July 31 for two XP-78 aircraft to be converted from lend-lease P-51s by using the Packard Merlin V-1650-3 engine and two-stage supercharger rated by the Air Force at 1,295 hp at 28,750 feet with 1,595 war emergency hp available to 17,000 feet.
Redesignated XP-51B in September, the first U.S. Merlin Mustang flew November 30, 1942, with a four-bladed Hamilton propeller and the carburetor intake below, instead of above, the engine. Even before tests, 2,290 Mustangs of this configuration were ordered, replacing 890 P-5lAs and adding 1,000 P-51Cs from a new assembly line at Dallas, Texas.
After severe cooling problems were overcome by an improved radiator, the first P-51B-l-NA was flown May 5, 1943. Armament still consisted of four .50-caliber guns, half that of a P-47, but the 440-mph top speed was the fastest of fighters then in combat. Even more important, the Mustang, with drop tanks, now had the range needed to accompany bombers to any target in Germany.
On July 6, 1943, the Air Force ordered that an 85- gallon fuel tank be added behind the cockpit, so a rebuilt P-51B was in the air by July 21, and these tanks were added by the AAF to 550 P-51B-5s, then redesignated P-51B-7. Such fuselage tanks became standard on all production models, beginning with the P-51B-10.
Mass production of the new Mustang at North American’s California and Texas factories increased rapidly. Inglewood built 1,988 P-51Bs which had the V-1650-3 Merlin, except for the improved V-1650-7s on the last 390 P-51B-15-NAs. In August, 1943, Dallas began delivery on 350 similar P-51C-l-NT Mustangs with the V-1650-3, but the remaining 1,400 P-51Cs made there in 1944 had the V-1650-7.
A plastic canopy with all-around vision was installed on two P-51D-1s converted from P-51B-10s and first flown November 17, 1943. This canopy, along with a modified wing holding six .50-caliber guns and 1,880 rounds, the V-1650-7, and a Hamilton propeller, appeared on the P-51D-5-NA, which replaced the B model at Inglewood in March 1944. A small dorsal fillet was added to the P-51D-10 model and fittings for ten 5-inch rockets were added to the P-51D-20. Two 1,000-pound bombs or 110-gallon drop tanks could be carried below their wings.
Mustang production increased to a high of 857 in the month of January 1945. By July 1945, 6,502 P-51D-NAs were built in California. The Texas factory built 1,454 P-51D-DTs interspersed with 1,337 P-51Ks (similar except for an Aeroproducts electric propeller), and ten TP-51D two-place trainers. Seventy-one P-51B-1s and 20 P-51C-1s were modified to F-6Cs in 1943, while 136 F-6Ds and 163 F-6Ks were built at Dallas beginning in November 1944.
Mustangs in Battle
American offensive operations from the United Kingdom were the new Mustangs’ first priority, and the first P-51B group there, the 354th, flew its first cross-channel sweep December 1, 1943. Soon the Mustangs could go anywhere the bombers could, and on March 4, 1944, they went all the way to Berlin. This made the P-51 the most important factor in winning the air war against Germany.
The Eighth Air Force got a new commander in January 1944, General Jimmy Doolittle, who extended the fighter mission from bomber escort to seeking out and destroying enemy fighters wherever they could be found in the air or on their bases. Mustangs steadily replaced other types after the invasion of France until 1945, when 14 P-51 groups and one P-47 group served the Eighth Air Force, responsible for strategic bombing, while 14 P-47 groups, three P-51 groups, and one P-38 fighter group served the Ninth Air Force, which operated in direct support of the ground armies.
The top Mustang group was the 357th, with 609 air and 106 ground kills from February 11, 1944, to April 25, 1945, while the 4th Group, which used Spitfires first, then P-47s, and finally P-51s in February 1944, had 583 air and 469 ground kills. Top Mustang aces were George Preddy with 25 victories, John C. Meyer, with 24, and Don Gentile, with 23.