Curtiss P-40 Warhawk in the context of "Packard V-1650 Merlin"

The North American Aviation P-51 Mustang is an American long-range, single-seat fighter and fighter-bomber used during World War II and the Korean War, among other conflicts. The Mustang was designed in 1940 by a team headed by James H. Kindelberger of North American Aviation (NAA) in response to a requirement of the British Purchasing Commission. The commission approached NAA to build Curtiss P-40 fighters under license for the Royal Air Force (RAF). Rather than build an old design from another company, NAA proposed the design and production of a more modern fighter. The prototype NA-73X airframe was completed on 9 September 1940, 102 days after contract signing, achieving its first flight on 26 October.

The Mustang was designed to use the Allison V-1710 engine without an export-sensitive turbosupercharger or a multi-stage supercharger, resulting in limited high-altitude performance. The aircraft was first flown operationally by the RAF as a tactical-reconnaissance aircraft and fighter-bomber (Mustang Mk I). In mid 1942, a development project known as the Rolls-Royce Mustang X, replaced the Allison engine with a Rolls-Royce Merlin 65 two-stage inter-cooled supercharged engine. During testing at Rolls-Royce's airfield at Hucknall in England, it was clear the engine dramatically improved the aircraft's performance at altitudes above 15,000 ft (4,600 m) without sacrificing range. Following receipt of the test results and after further flights by USAAF pilots, the results were so positive that North American began work on converting several aircraft developing into the P-51B/C (Mustang Mk III) model, which became the first long-range fighter to be able to compete with the Luftwaffe's fighters. 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.

The Desert Air Force (DAF), also known chronologically as Air Headquarters Western Desert, Air Headquarters Libya, the Western Desert Air Force, and the First Tactical Air Force (1TAF), was an Allied tactical air force created from No. 204 Group RAF under RAF Middle East Command in North Africa in 1941 to provide close air support to the British Eighth Army against Axis forces. Throughout the Second World War, the DAF was made up of squadrons from the Royal Air Force (RAF), the South African Air Force (SAAF), the Royal Australian Air Force (RAAF), the United States Army Air Forces (USAAF) and other Allied air forces.

In October 1941, the Western Desert Air Forces had 16 squadrons of aircraft (nine fighter, six medium bomber and one tactical reconnaissance) and fielded approximately 1,000 combat aircraft by late 1941. By the time of the Second Battle of El Alamein, the DAF fielded 29 squadrons (including nine South African and three USAAF units) flying Boston, Baltimore and Mitchell medium bombers; Hurricane, Kittyhawk, Tomahawk, Warhawk and Spitfire fighters and fighter-bombers. There were over 1,500 combat aircraft, more than double the number of aircraft the Axis could field.

The First American Volunteer Group (AVG; Chinese: 中華民國空軍美籍志願大隊) of the Republic of China Air Force, nicknamed the Flying Tigers (飛虎隊), was formed to help oppose the Japanese invasion of China. Operating in 1941–1942, it was composed of pilots from the United States Army Air Corps (USAAC), Navy (USN), and Marine Corps (USMC), and was commanded by Claire Lee Chennault. Their Curtiss P-40B Warhawk aircraft, marked with Chinese colors, flew under American control. Recruited under President Franklin Roosevelt's authority before Pearl Harbor, their mission was to bomb Japan and defend the Republic of China, but many delays meant the AVG first flew in combat after the United States and Japan declared war.

The group consisted of three fighter squadrons of around 30 aircraft each that trained in Burma before the American entry into World War II to defend the Republic of China against Japanese forces. The AVG were officially members of the Republic of China Air Force. The group had contracts with salaries ranging from $250 a month for a mechanic to $750 for a squadron commander, roughly three times what they had been making in the U.S. forces. While it accepted some civilian volunteers for its headquarters and ground crew, the AVG recruited most of its staff from the U.S. military.