The Rolls-Royce Derwent was one of the first turbojet engines built in large series after World War II to equip various military and civilian aircraft. Derived from the 1943 Rolls-Royce Welland engine, the Derwent features the same constructive layout of designed by Frank Whittle, with single-stage centrifugal compressor. Its technical development, started in 1944, was closely related to the larger and more powerful Rolls-Royce Nene. The Derwent remained in production up to the early 1950s in various construction series, with continuous technical and performance improvements. In Italy it was used to equip the Aerfer Sagittario 2, the first Italian aircraft to exceed the speed of sound on 4 December 1956.