The Comet was removed from service and tested to discover the cause. Design flaws, including dangerous stresses at the corners of the square windows were noted. As a result, the Comet was redesigned into models 2, 3, and in 1958 the Comet 4. But meanwhile other aircraft designers had their own jets, the Boeing 707 in 1957 and in 1960 the Douglas DC-8. The American jets were larger, faster, longer-ranged, and more cost-effective than the Comet. In 1960, as part of a consolidation of the British aerospace industry, de Havilland was bought by Hawker Siddeley. Aviation author Bill Withun concluded that the Comet had pushed "'state-of-the-art' beyond its limits." The only complete remaining Comet 1 is displayed at the RAF Museum Cosford.