The Charles M. Schulz - Sonoma County Airport (STS) has a long history in Sonoma County. In 1941 the County purchased 339 acres of agricultural land and began constructing a runway using grant funds from the Civil Aeronautics Authority (predecessor to the Federal Aviation Administration). The U.S. Army took over in 1942 and added 826 acres, extended the original runway, built a second runway, added taxiways, apron areas, and other facilities. Two of the hangars constructed by the Army remain in use today. Between February 1943 and January 1946, the U.S. Fourth Air Corps operated the Sonoma County Airport. At that time, it was known as the Santa Rosa Army Airfield and was used primarily to train fighter groups and squadrons. At its peak, some 300 to 500 aircraft and 10,000 personnel were based on the army field.