Just before daylight on Sunday June 25, 1950, the North Korea People's Army crossed the 38th parallel of latitude, into the southern portion of Korea. The North Koreans, supported by the Russians and then later the Chinese, invaded and tried to conquer South Korea, which was supported by the United States and other countries operating under the flag of the United Nations. Early in the war, the Mustang resumed its combat career for its endurance and ability to operate from frontline air-strips impossible for the jet fighters, and above all, its availability, rendered the P-51 well-suited for Korean service.
The advance of the North Koreans was accompanied by widespread air activity of tactical nature, the arrival of the U.S. heavy bombers led to an intensive air war against North Korea's lines of communication and supply dumps. However, threatened intervention by Communist China led to the adoption by the U.N. forces of political restraints on air and surface operations, in accordance with which the crossing of the Yalu River under any circumstances was forbidden. This provided our opponents with a sanctuary in which they could stockpile supplies and build up air bases for an air force making increased use of modern Russian aircraft, notably the MIG-15 jet fighter.
By the early 1950's, air-to-air missiles began to be added to the arsenal of fighter aircraft weapons, initially supplementing machine guns and eventually overtaking them in importance. Rockets under development were based on the German-designed R-24 air-to-air rocket that had been used against Allied bombers during the Second World War. The rockets that evolved from this development program were designated the 2.75 inch Folding Fin Aircraft Rocket (FFAR). The rockets had an effective range of about 2,000 yards and a high explosive warhead. Several fighter aircraft were armed with these rockets, including the North American F-86D with an under fuselage retractable tray containing 24 FFARs, and the Lockheed F-94C with 24 FFARs in the nose. By the fall of 1950, North Korea was a beaten enemy. U.N. Forces were within 50 odd miles of the Yalu River, North Korea's northern boundary. Pyongyang, the capital, was in Allied hands. Communist China, unwilling to tolerate a predominately U.S. force on its borders, entered the war.
Though lacking in modern war technology, China was able to muster and deploy manpower in overwhelming numbers. U.N. Forces again found themselves in retreat down the Korean peninsula. Unlike the previous year, however, this was a strategic withdrawal, designed to remain intact as a fighting force, while wearing down the enemy. In the spring of 1951, the North Korean-Chinese offensive ground to a haltU.N. forces went over to the offensive, and once again began a steady advance up the peninsula. At approximately the location of the national boundary between the two Koreas, the 38th parallel of latitude, North Korea and China requested an armistice. A cease-fire ensued, and a demilitarized zone was established which still exists.