From 1950, North Koreans flew the Soviet-made MiG-15 jet fighters which introduced the near-sonic speeds of swept wings to air combat. Though an open secret during the war, the most formidable pilots today now admit that they were experienced Soviet Air Force pilots, a casus belli deliberately overlooked by the UN allied forces who suspected the use of Russians but were reluctant to engage in open war with the Soviet Union and the People's Republic of China.
