<P> In 1921, Croydon Airport, London was the first airport in the world to introduce air traffic control . </P> <P> In the United States, air traffic control developed three divisions . The first of air mail radio stations (AMRS) was created in 1922 after World War I when the U.S. Post Office began using techniques developed by the Army to direct and track the movements of reconnaissance aircraft . Over time, the AMRS morphed into flight service stations . Today's flight service stations do not issue control instructions, but provide pilots with many other flight related informational services . They do relay control instructions from ATC in areas where flight service is the only facility with radio or phone coverage . The first airport traffic control tower, regulating arrivals, departures and surface movement of aircraft at a specific airport, opened in Cleveland in 1930 . Approach / departure control facilities were created after adoption of radar in the 1950s to monitor and control the busy airspace around larger airports . The first air route traffic control center, which directs the movement of aircraft between departure and destination was opened in Newark, NJ in 1935, followed in 1936 by Chicago and Cleveland . </P> <P> The primary method of controlling the immediate airport environment is visual observation from the airport control tower . The tower is a tall, windowed structure located on the airport grounds . Air traffic controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 5 to 10 nautical miles (9 to 18 km) depending on the airport procedures . </P> <P> Surveillance displays are also available to controllers at larger airports to assist with controlling air traffic . Controllers may use a radar system called secondary surveillance radar for airborne traffic approaching and departing . These displays include a map of the area, the position of various aircraft, and data tags that include aircraft identification, speed, altitude, and other information described in local procedures . In adverse weather conditions the tower controllers may also use surface movement radar (SMR), surface movement guidance and control systems (SMGCS) or advanced SMGCS to control traffic on the manoeuvring area (taxiways and runway). </P>

The atc position which exercises control over taxiing aircraft is