The Korean War (1950-1953) -- The other guys...
When North Korea invaded South Korea in June of 1950, igniting the Korean War, the NK Air Force was small and inexperienced. There were two main combat aircraft: The Ilyushin Il-10 (NATO code name: Beast) ground attack aircraft and the Yakovlev Yak-9 (NATO code name: Frank). Both of these aircraft types were World War II-era Soviet designs with liquid-cooled V-12 piston engines. As in the war on the ground, the North Koreans had the advantage of surprise and enjoyed early successes. But the U.S. intervened quickly with U.S. Air Force aircraft from still-occupied Japan and from U.S. Navy carriers in the region. The NK Air Force was quickly obliterated, and the skies belonged to United Nations air forces.
The USSR reacted quickly to aid the North Koreans and Russian pilots began covertly flying combat missions in aircraft with NK markings, creating the fiction that the Soviets were not engaged in the war. The Soviets also began training North Korean pilots on the Mikoyan-Gurevich MiG-15 (NATO code name: Fagot), which in 1950 was among the most advanced fighter aircraft in the world.
The MiG-15 had first flown in 1948 and was powered by a Klimov RD-45 turbojet engine, a copy of the UK Rolls-Royce Nene. It was a transonic fighter with a top speed close to the speed of sound and was heavily armed with two 23mm cannon and a single 37mm cannon.
In 1949, an improved version of the MiG-15 first flew and was designated the MiG-15bis. It was powered by a more powerful Klimov VK-1A engine with 5.950 lbs. of the thrust rather than the 5,000 lbs. of the MiG-15.
The MiG-15 and -15bis remained the primary fighter aircraft on the North Korean side for the entire war. A large proportion of the combat missions continued to be flown by Soviet pilots and they were joined by pilots from China. Participation in the air war by the USSR and China continued to be covert for the entire war, although the UN side knew perfectly well what was going on; presumably they chose not to publicize the fact to avoid expanding the war.
https://en.wikipedia.org/wiki/Korean_War (see section on the air war)