In the summer of 1941, the US Army Air Forces (USAAF) received two Mustang Is under the designation XP-51. Although flight tests of the new fighter showed promise, the USAAF did not immediately order the Mustang. After the personal intervention of Gen. Hap Arnold, however, the USAAF retained 55 Mustangs from a British order. Most of these became F-6A photo-reconnaissance aircraft, which equipped the first USAAF Mustang units, the 154th and 111th Observation Squadrons in North Africa in the spring of 1943.

In March 1942 the USAAF accepted the first production P-51A fighters. Although excellent at lower levels, the P-51A’s Allison engines severely limited performance at high altitude. The USAAF employed P-51As in the China-Burma-India theater, where most combat took place at low altitude.

In April 1942 the USAAF ordered an attack version equipped with dive brakes and bomb racks, the A-36 Apache. A-36s entered combat in June 1943 and served in North Africa, Italy and India.

A winning combination

In the fall of 1942, Mustangs in the United States and Great Britain were experimentally fitted with British Merlin engines. One in the United States flew a remarkable 441 mph at 29,800 feet — about 100 mph faster than the P-51A at that altitude. Mass production of the Merlin-powered P-51B and P-51C soon followed (nearly identical, North American produced the “B” in Inglewood, Calif., and the “C” in Dallas, Texas).

In December 1943 the first P-51B/C Mustangs entered combat in Europe with the 354th Fighter Group “Pioneers.” By the time of the first U.S. heavy bomber strike against Berlin in March 1944, the USAAF fielded about 175 P-51B/C Mustangs. Along with P-38 Lightnings, these P-51s provided sorely needed long-range, high-altitude escort for the U.S. bombing campaign against Germany.

The P-51D incorporated several improvements, and it became the most numerous variant with nearly 8,000 being built. The most obvious change was a new “bubble-top” canopy that greatly improved the pilot’s vision. The P-51D also received the new K-14 gunsight, an increase from four to six .50-cal machine guns, and a simplified ammunition feed system that considerably reduced gun jams.

P-51 hitting Luftwaffe training bases

The P-51D arrived in quantity in Europe in the spring of 1944, becoming the USAAF’s primary long range escort fighter.

Pete Feigal, Former Pro Military Artist, explains on Quora;

‘One of the great strengths of the P-51, when they arrived, was that they could fly deep enough into Germany to hit the Luftwaffe training bases, killing the young trainees, the “Floaters,” or “Clay Pigeons,” as was the slang, previously believed to be too distant from England and immune from fighter raids…wrong. Although flown with fewer aircraft and numbers of sorties, these missions were a priority after bomber escort, and get way too little focus. Combined with the rapidly dwindling (low octane) synthetic fuel, this devastated the German’s training “program,” and spelled “doom” for the Luftwaffe.’

He adds;

‘Robert S. Johnson, 27 victories in P-47s, 56th FG, America’s #2 ace in the ETO, explained in an interview with Military History Magazine;

‘“The P-51s had the advantage of longer range, and they were able to hit even the training schools, hitting boys just learning to fly. As the war dragged on, many of the old German veterans had been killed–so much of the experience was gone.”’