Missiles had long been regarded the ideal platform for nuclear weapons, and were potentially a more effective delivery system than bombers. Starting in the 1950s, medium-range ballistic missiles and intermediate-range ballistic missiles ("IRBM"s) were developed for delivery of tactical nuclear weapons, and the technology developed to the progressively longer ranges, eventually becoming intercontinental ballistic missiles (ICBMs). On October 4, 1957, the Soviet Union showed the world that they had missiles able to reach any part of the world when they launched the Sputnik satellite into Earth orbit. The United States launched its first satellite Explorer 1 on January 31, 1958.