Soviet rocketry commenced in 1921 with development of Solid-fuel rockets, which resulted in the development of the Katyusha rocket launcher. Rocket scientists and engineers, particularly Valentin Glushko and Sergei Korolev, contributed to the development of Liquid-fuel rockets, which were first used for fighter aircraft and later for ballistic missiles, and space exploration. Progress was greatly augmented by the reverse engineering of Nazi German technology captured by westward-moving troops during the final days of World War II and the immediate period following, though after 1947 their influence was marginal. Developments continued in the 1950s with a variety of ICBMs and resulted in the launch of Sputnik 1 in 1957, the first artificial Earth satellite ever launched.