The frontline Soviet fighter of the Korean War was, ironically, built with the help of the British.

During the Second World War, the British, Americans and Germans did extensive research into jet engines. The Soviet Union, however, was hampered by the destruction caused by the Nazi invasion (and also by political purges launched by Stalin) and fell behind. The first Soviet jet fighter, the MiG-9, was produced by the Mikoyan-Guryevich design bureau late in 1946. It was based largely on research data and engineers that had been captured in Germany, and was powered by a Russian copy of the German HeS-011 jet engine. Although the plane reached operational status and around 600 MiG-9s were deployed, they never worked very well. Soviet designers found that they could produce pretty good airframes, but they were seriously lagging in jet-engine technology and know-how to power them.
And so they made a desperate move. Towards the end of 1946, at the urging of aircraft designer Alexander Yakovlev, the Soviets approached the British with an offer to buy some of their new Nene jet engines, the same ones being licensed to the Americans for their F9F Panther. Reportedly remarking “What sort of fool would sell their best secrets to their enemy?”, Stalin thought the proposal was ridiculous but agreed to allow it anyway. It was not as crazy an idea as it sounded, though: the Cold War hadn’t reached fever pitch yet, the British government was now under the Labor Party, which had not taken as hard a line against the Russians as Winston Churchill’s Tories had—and Prime Minister Clement Attlee was desperate for any source of income to revive the UK’s shattered economy.
As part of the negotiations, several Soviet technicians were brought to England and given a tour of the Rolls-Royce factory where the engines were made. As a precaution in case the deal fell through, the Russians cleverly wore soft-soled shoes and then made sure to walk around the area where the engine parts were being milled so the shavings became embedded. This, they figured, would at least allow them to figure out what materials the engines used.
But the deal did go through, and in 1947 the Soviet manufacturing bureau headed by Vladimir Klimov won the rights to produce licensed copies of the Nene (though they never paid any of the licensing fees). The Soviet copy was known as the Klimov RD-45. It was better than anything the USSR could have produced on its own at the time.
Immediately the order went out to replace the MiG-9 with a new version using the British-designed engine. To save time, Mikoyan designers took the already-existing MiG-9 as their starting point, and modified it to take advantage of the more powerful engine, using much of the data they had gathered from the Nazi Focke Wulf Ta-183 design. The MiG-9’s straight wings were swept back and the tail was redesigned. The new fighter was designated MiG-15, and NATO gave it the codename “Fagot”. (During the entire Cold War, Soviet bombers received NATO codenames that began with a B, while fighter names began with an F: one-syllable names denoted a piston-engined aircraft, while two-syllable names indicated a jet.) A short time later, an improved version appeared which was designated MiG-15bis (“bis” was engineering shorthand for “second version”), powered by a better-engineered Russian copy of the Nene, the VK-1.
It proved to be a superb fighter. Its low weight-to-power ratio and its speed of 670mph made it fast and maneuverable, and its two 23mm and one 37mm cannons gave it enough firepower to handle any American bomber. It tended to become unstable near Mach 1, though, which the Soviets solved with typical brute practicality—they installed speed brakes that automatically deployed at Mach 0.9.
The new fighter entered production in December 1948, with one version going to the Soviets and an export version which was shipped to other countries in the Soviet Bloc. This included the Chinese Communists, who were still fighting skirmishes with the US-backed Chinese Nationalists. The MiG-15’s first air victory (the Chinese copies were designated J-2) came in April 1950, when a Chinese pilot shot down a Nationalist piston-engined P-38 Lightning.
The MiG’s real test came just two months later when the Korean War broke out. Soviet MiG-15s appeared over Korea, flown by North Korean pilots, Chinese Communist “volunteers”, and, in a top secret program of testing and evaluation, veteran Russian pilots. The sky over the Chinese border became known as “MiG Alley”, and the nimble little Soviet fighters proved to be superior to anything the Americans had, including the newest F-80s and F-84s. The MiGs had established air superiority, and so many B-29 bombers were shot down that the UN had to stop flying daylight bombing missions over Korea.
The United States, meanwhile, rushed its own F-86 Sabre into production and began deploying it to Korea, where it evened out the odds. At the time, American F-86 pilots claimed a 10-to-1 kill ratio against the MiGs, but later research seems to show that although the Sabre was the better dogfighter and the Chinese and Korean MiG pilots were poorly-trained, this rate of success was probably exaggerated. The Russian pilots, meanwhile, most of them already aces from their World War II experience, claimed a 10-to-1 kill ratio against the American F-86s—which was also probably exaggerated.
After the Korean War, MiG-15s continued in frontline service with many countries, especially in the Middle East, through the 1960s. By the 70s they had been demoted to trainers. In all, around 20,000 MiG-15s were built, for about two dozen countries in the Soviet Bloc and a number of neutral nations as well. The North Koreans still use them as trainers.
After the collapse of the Soviet Union in 1991 and the emergence of China as an economic power, vintage MiG-15 aircraft became available on the international market. Today there are over 50 airworthy MiG-15s in private hands in the US, and they are now common as museum displays, especially the two-seat UTI trainer version.
In 1985, an American air museum in Arizona purchased a MiG-15UTI trainer from the Chinese government for $130,000. The serial number of this plane is missing, however, which makes it difficult to trace its history. It may have been made in the USSR and sold to China, or it may have been a Chinese-made J-2 copy. In any case, a year later, the museum traded the MiG to the Smithsonian in exchange for three US Navy T-28 trainers. Today, this Chinese MiG is on display at the Udvar-Hazy Center.
During the Korean War the Americans were desperate to have a close look at the MiG-15, so they showered North Korea with leaflets offering a $100,000 reward to any pilot who defected to the West with his fighter plane. In November 1953, after the war had ended, North Korean pilot No Kum-Sok landed his MiG-15bis at an airbase in South Korea. That North Korean fighter is now on display at the US Air Force Museum in Dayton.