[20][nb 2] The other feature was a new cooling arrangement positioned aft (single ducted water and oil radiators assembly) that reduced the fuselage drag and effects on the wing.

Later,[22] after much development, they discovered that the cooling assembly could take advantage of the Meredith effect, in which heated air exited the radiator with a slight amount of jet thrust.

[16] To ensure uninterrupted delivery, Colonel Oliver P. Echols arranged with the Anglo-French Purchasing Commission to deliver the aircraft and NAA gave two examples (41-038 and 41-039) to the USAAC for evaluation.

In November 1941, NAA studied the possibility of using it, but fitting its excessive length in the Mustang would require extensive airframe modifications and cause long production delays.

[37] Initially, the Mustang's steadfast champion, USAAC/F Assistant Air Attaché Major Thomas Hitchcock, was concerned that the USAAF had little or no interest in the potential of the P-51A and its development with the Merlin engine.

Conversion to the two-stage supercharged and intercooled Merlin 60 series, over 350 lb (160 kg) heavier than the single-stage Allison, driving a four-bladed Hamilton Standard propeller, required moving the wing slightly forward to correct the aircraft's center of gravity.

Army Co-operation Command used the Mustang's superior speed and long range to conduct low-altitude "Rhubarb" raids over continental Europe, sometimes penetrating German airspace.

The V-1710 engine ran smoothly at 1,100 rpm, versus 1,600 for the Merlin, enabling long flights over water at 50 ft (15 m) altitude before approaching the enemy coastline.

[47] The RAF gained a significant performance enhancement at low altitude by removing or resetting the engine's manifold pressure regulator to allow overboosting, raising output as high as 1,780 horsepower at 70 in Hg.

[51] Despite RAF and Luftwaffe experience with daylight bombing, the USAAF still incorrectly believed in 1942 that tightly packed formations of bombers would have so much firepower that they could fend off fighters on their own.

[54] In January 1943, at the Casablanca Conference, the Allies formulated the Combined Bomber Offensive (CBO) plan for "round-the-clock" bombing – USAAF daytime operations complementing the RAF nighttime raids on industrial centers.

In June 1943, the Combined Chiefs of Staff issued the Pointblank Directive to destroy the Luftwaffe's capacity before the planned invasion of Europe, putting the CBO into full implementation.

[60] The Luftwaffe's twin-engined Messerschmitt Bf 110 heavy fighters brought up to deal with the bombers proved to be easy prey for the Mustangs, and had to be quickly withdrawn from combat.

[citation needed] At the start of 1944, Major General James Doolittle, the new commander of the 8th Air Force, released most fighters from the requirement of flying in close formation with the bombers, allowing them free rein to attack the Luftwaffe wherever it could be found.

The P-51, particularly with the advent of the K-14 gyro gunsight and the development of "Clobber Colleges"[63] for the training of fighter pilots in fall 1944, was a decisive element in Allied countermeasures against the Jagdverbände.

[citation needed] Given the overwhelming Allied air superiority, the Luftwaffe put its effort into the development of aircraft of such high performance that they could operate with impunity, but which also made bomber attack much more difficult, merely from the flight velocities they achieved.

The widespread destruction and high number of casualties from these raids caused many Japanese to realize that their country's military was no longer able to defend the home islands.

[77][78][79] In Tokyo, Osaka, Nagoya, Yokohama, Kobe, and Kawasaki, "over 126,762 people were killed ... and a million and a half dwellings and over 105 square miles (270 km2) of urban space were destroyed.

[83] Due to the lack of Japanese air opposition to the American bomber raids, VII Fighter Command was solely tasked with ground-attack missions from July.

[92]In the aftermath of World War II, the USAAF consolidated much of its wartime combat force and selected the P-51 as a "standard" piston-engined fighter, while other types, such as the P-38 and P-47, were withdrawn or given substantially reduced roles.

After the first North Korean invasion, USAF units were forced to fly from bases in Japan and the F-51Ds, with their long range and endurance, could attack targets in Korea that short-ranged F-80 jets could not.

Though his aircraft was heavily damaged and he was wounded during the first pass on the column, he turned his F-51 around and deliberately crashed into the convoy at the cost of his life, and was posthumously awarded the Medal of Honor.

In 1967 and again in 1972, the USAF procured batches of remanufactured Mustangs from Cavalier, most of them destined for air forces in South America and Asia that were participating in the Military Assistance Program (MAP).

These aircraft were remanufactured from existing original F-51D airframes fitted with new V-1650-7 engines, a new radio, tall F-51H-type vertical tails, and a stronger wing that could carry six 13 mm (0.50 in) machine guns and a total of eight underwing hardpoints.

[99] Cavalier Mustang 68-15796 survives at the Air Force Armament Museum, Eglin AFB, Florida, displayed indoors in World War II markings.

[10] During the war, a Mustang cost about $51,000,[101] while many hundreds were sold postwar for the nominal price of one dollar to signatories of the Inter-American Treaty of Reciprocal Assistance, ratified in Rio de Janeiro in 1947.

He sold the Mustang to Charles F. Blair Jr (future husband of Maureen O'Hara), who renamed it Excalibur III and used it to set a New York-to-London (about 3,460 miles or 5,570 kilometres) record in 1951: 7 hr 48 min from takeoff at Idlewild to overhead London Airport.

A number of conversions included a Cavalier Mustang specialty: a "tight" second seat added in the space formerly occupied by the military radio and fuselage fuel tank.

In the late 1960s and early 1970s, when the United States Department of Defense wished to supply aircraft to South American countries and later Indonesia for close air support and counterinsurgency, it paid Cavalier to return some of their civilian conversions back to updated military specifications.

Except for the small numbers assembled or produced in Australia, all Mustangs were built by North American initially at Inglewood, California, but then additionally in Dallas, Texas.