The British de Havilland Comet first flew in 1949 and is noted as the world's first commercial jet airliner. Early models suffered from catastrophic metal fatigue and the aircraft was redesigned. The Comet 4 series subsequently enjoyed a long and productive career of over 30 years. The Hawker Siddeley Nimrod, the military derivative of the Comet airliner, is still in service. In 2007, the original decades-old airframes were being rebuilt with new wings and engines to produce the Nimrod MRA 4, expected to serve with Britain's Royal Air Force until the 2020s, more than 70 years after the Comet's first flight.