Mikoyan-Gurevich MiG-15bis, Korean war. Part one.

The Soviets had secretly been deploying MiG-15 squadrons close to the North Korean border, in the Manchurian province of Antung in August 1950 and were already training Chinese pilots in mainland China when China entered the war supporting North Korea. By October, the Soviet Union had agreed to provide state-of-the-art MiG-15 fighters together with trained crews to flight them. At the same time, agreed to supply both the Chinese and North Koreans with their own MiG-15s and train their pilots.
In November, the 50th IAD (Soviet Fighter Regiment) joined the war with its MiG-15s and their noses painted red and in North Korean Markings and more units were moved to the Far East Theatre.
Despite many successful clashes where the MiG-15 appeared victorious, on 9th November the first loss of a MiG-15 took place when a Grumman F8F that had took-off from the USS Philippine Sea carrier shot down a MiG-15.
In order to counter the MiG-15 menace, three squadrons equipped with the F-86 Sabre, America's only swept-wing fighter of the time, were rushed to the Far East in December 1950. On 17th December Lt.Col. Bruce H. Hinton forced Major Yakov N. Yefromeyenko to eject from his burning MiG. During the following days both sides clashed with both sides exaggerating their claims on aerial victories. The USAF claimed eight MiGs and the Soviets claimed twelve F-86s when actual losses were three MiGs and at least four F-86s.
That same month, the Soviet 324th IAD Division arrived to Antung, the main base of the Soviet units, formed mainly with elite units, among them Col. Ivan Kozhedub, who was the top Soviet ace of the World War II and it wasn't until April 1951 that they entered into action.
The main mission of the MiG-15 wasn't to clash against the F-86 but to intercept the large formations of B-29 Superfortress. One of those action took place on 12th April 1951 when a formation of 44 MiG-15s faced an USAF formation of three squadrons of B-29 Superfortress (44 bombers) escorted by 96 F-80 and F-84 fighters. The Soviets managed to lure the escorts away and shot down three B-29 and badly damage 7 bombers more and 11 F-80 shot down. Due to that action, which is known as the "Black Thursday" in the USAF, bomber operations were put on hold for three months, switching from day bombings in large formations to night bombing in small formations.

Sources:
1. https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-15#The_Korean_War_(1950–1953)
2. https://en.wikipedia.org/wiki/MiG_Alley
3. Salamander Books - The Complete Book of Fighters