During the Korean War, the Corsair was used mostly in the close-support role. The AU-1 Corsair was developed from the F4U-5 and was a ground-attack version which normally operated at low altitudes: as a consequence the Pratt & Whitney R-2800-83W engine used a single-stage, manually controlled supercharger, rather than the two-stage automatic supercharger of the -5. The versions of the Corsair used in Korea from 1950 to 1953 were the AU-1, F4U-4B, -4P, and -5N and 5-NL. There were dogfights between F4Us and Soviet-built Yakovlev Yak-9 fighters early in the war, but when the enemy introduced the Mikoyan-Gurevich MiG-15, the Corsair was outmatched. On 10 September 1952, a MiG-15 made the mistake of getting into a turning contest with a Corsair piloted by Marine Captain Jesse G. Folmar, with Folmar shooting the MiG down with his four 20 mm cannon. In turn, four MiG-15s shot down Folmar minutes later; Folmar bailed out and was quickly rescued with little injury.