The First Air Traffic Control Tower. 

The world's first air traffic control (ATC) tower opened in February 1920.
The new facility was located at London's then-main airport, Croydon.

The now-decommissioned airfield was then the only international airport in the UK in the interwar years. As civilian air travel grew after the First World War, the UK's Air Ministry wanted to find a way of safely organizing the growing number of flights.

Previously, airports had limited radio offices and 'aerial lighthouses' on-site to assist with aircraft movements. Meanwhile, pilots utilized visual aids to guide them safely to the airport.

Described as an "essential" development, the 'Aerodrome Control Tower,' as it was then known, was commissioned on February 25th, 1920. The Air Ministry stated that the wooden tower had to be "erected 4 meters above ground level: "It needed "large windows placed on all four walls, with a wind-vane to be fitted to the hut's roof with a geared-down indicator placed inside, enabling the control officer to read changes of wind."

Civil Aviation Traffic Officers provided essential air traffic, weather, and local information for flight crews. Flights would be tracked with radio navigation and then marked onto paper maps using pins and flags. Radio-telephony had developed during the First World War and lent itself well to the support of commercial air services.

As aviation developed during World War Two, numerous new technologies were introduced, many of which remain today. These include radio localization, two-way radio communication, and paper flight progress strips to track an aircraft's movement at the airport and in the air.

By 1944, ATC towers became compulsory at airports. Croydon's tower would become the blueprint for all future examples.