On July 27, 1949, the world quite abruptly became a very small place. The new scale, which drew together cities and coastlines that had for millennia existed on basically separate planets, came courtesy of the de Havilland Comet, the first commercial jet aircraft to enter production. With its pressurized cabin, it could travel as high as 42,000 feet, and, courtesy of four turbojet engines offering 22,000 Newtons of thrust each, it cruised at 460 miles per hour.
The next best thing until the Comet arrived was the propeller-driven DC-3, which could hit 250 mph, at best. Air travel in its 1930s and 40s infancy was characterized by short but exhausting flights that took a long time (relatively) and were frequently marred by gnarly weather characteristic of lower altitudes. At the time, jet engines were thought to be too inefficient and fuel hungry and too unreliable to be seriously considered for commercial aviation.
Nonetheless, Sir Geoffrey de Havilland, whose company had gotten its start producing biplanes, took it as a challenge. In 1945, de Havilland was awarded a contract from the UK government to design and produce a mailplane capable with a pressurized cabin capable of transatlantic flight and cruising speeds of at least 400 mph. In 1945, before a design team had even been formed at de Havilland, the British Overseas Airways Corporation made an order for 10 turbojet aircraft.
The Comet began regular service in 1952 and, by 1953, BOAC was flying nine Comets per week from London to distant locales such as Tokyo, Singapore, and Johannesburg. More airlines placed orders.
Then it all went wrong, at least for a time. There were two fatal Comet accidents in 1953, one of which involved an aircraft disintegrating in mid-air while passing through a thunderstorm. In 1954, another Comet crashed after takeoff from Rome following an explosive decompression. The planes were grounded and several inquiries took place, with the major finding being that the aircraft's hull was too weak to deal with flight stresses that were still poorly understood at the time of the plane's development.
Many of the Comet 1s were scrapped, to be later replaced by a more robust version, the Comet 2. According to Comet! The World's First Jet Airliner, the final Comet 4 left service in 1997. It's operator then was the UK's Royal Aircraft Establishment, which used it to collect aeronautical data.