London's efficient transport system is controlled and operated by a public body called London Transport. Its network extends slightly beyond Greater London and consists primarily of bus lines and underground and surface railways. In addition, all of Britain's mainline railways radiate from central London. Principal rail stations include Charing Cross, Victoria, Paddington, and Waterloo.
London's subways make up about two-fifths of the city's 250-mile (400-km) railway system. Some lines run in brick tunnels just below the surface and make up a system called the underground. The first such line was opened in 1863. Later lines were built in deep, metal-lined tunnels and are popularly called tubes. During World War II passenger stations in the tubes served as air-raid shelters.
London has three international airports. Heathrow, London's main airport, is west of the city. It is one of the largest and busiest airports in western Europe, serving millions of passengers each year; for international flights it is the world's busiest airport. Gatwick Airport, south of London, was opened in 1958 to ease the congestion at Heathrow. Gatwick is adjacent to the main London-to-Brighton railway line. The third airport serving London is Stansted, northeast of the city.