Osan Air Base is one of two major airfields operated by the U.S. in Korea and the only USAF facility in the Republic of Korea (ROK) entirely planned and built by the U.S. from scratch during the Korean War. The base is located 4.7 miles southwest of the town of Osan, for which it is named, and 40 miles south of Seoul, the capital city. Prior to the invasion of the Republic of Korea by the North Korean communists in 1950, the area consisted of several tiny farming villages near the hillsides and a large number of rice paddie areas where the runway now lies. A large ginko tree marked the village square of one of these villages and still stands on a hill in the base golf course.