A cruise missile is a guided missile used against terrestrial targets that remains in the atmosphere and flies the major portion of its flight path at approximately constant speed. Cruise missiles are designed to deliver a large warhead over long distances with high precision; that is, small circular error probability. Modern cruise missiles are capable of travelling at supersonic or high subsonic speeds, are self-navigating, and are able to fly on a non-ballistic, extremely low-altitude trajectory.
The idea of an "aerial torpedo" was shown in the British 1909 film The Airship Destroyer, where flying torpedoes controlled wirelessly are used to bring down airships bombing London.
In 1916, Lawrence Sperry built and patented an "aerial torpedo", a small biplane carrying a TNT charge, a Sperry autopilot and a barometric altitude control. Inspired by these experiments, the United States Army developed a similar flying bomb called the Kettering Bug. Germany had also flown trials with remote-controlled aerial gliders (Torpedogleiter) built by Siemens-Schuckert beginning in 1916.
In the period between the World Wars the United Kingdom developed the Larynx (Long Range Gun with Lynx Engine), which underwent a few flight tests in the 1920s.
In the Soviet Union, Sergei Korolev headed the GIRD-06 cruise missile project from 1932 to 1939, which used a rocket-powered boost-glide bomb design. The 06/III (RP-216) and 06/IV (RP-212) contained gyroscopic guidance systems. The vehicle was designed to boost to 28 km altitude and glide a distance of 280 km, but test flights in 1934 and 1936 only reached an altitude of 500 meters.
In 1944, Germany deployed the first operational cruise missiles in World War II. The V-1, often called a flying bomb, contained a gyroscope guidance system and was propelled by a simple pulsejet engine, the sound of which gave it the nickname of "buzz bomb" or "doodlebug". Accuracy was sufficient only for use against very large targets (the general area of a city), while the range of 250 km was significantly lower than that of a bomber carrying the same payload. The main advantages were speed (while not sufficient to outperform contemporary interceptors) and expendability. The production cost of a V-1 was only a small fraction of that of a V-2 supersonic ballistic missile, carrying a similar-sized warhead. Unlike the V-2, however, the initial deployments of the V-1 required stationary launch ramps which were susceptible to bombardment. Nazi Germany, in 1943, also developed the Mistel composite aircraft program, which can be seen as a rudimentary air-launched cruise missile, where a piloted fighter-type aircraft was mounted atop an unpiloted bomber-sized aircraft that was packed with explosives to be released while approaching the target. Bomber-launched variants of the V-1 saw limited operational service near the end of the war, with the pioneering V-1's design reverse-engineered by the Americans as the Republic-Ford JB-2 cruise missile.