A cruise missile is a guided missile the major portion of whose flight path to its target (a land-based or sea-based target) is conducted at approximately constant velocity; that relies on the dynamic reaction of air for lift, and upon propulsion forces to balance drag. Cruise missiles are designed to deliver a large warhead over long distances with high accuracy. Modern cruise missiles can travel at supersonic or high subsonic speeds, are self-navigating, and can fly on a non-ballistic, extremely low altitude trajectory. They are distinct from unmanned aerial vehicles (UAV) in that they are used only as weapons and not for reconnaissance. In a cruise missile, the warhead is integrated into the vehicle and the vehicle is always sacrificed in the mission.
Cruise missile designs fundamentally derive from the German V-1 of World War II. Advances in transistor and computer technology have contributed to self-correcting avionic and aeronautical designs that allow missiles to be guided in flight, as opposed to only at launch. These advances developed into guided missiles and guided bombs, and later into the modern cruise missile.
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 patented and built an “aerial torpedo”, a small biplane carrying a TNT charge, a Sperry autopilot and a barometric altitude control. Inspired by these experiments, the US Army developed a similar flying bomb called the Kettering Bug. Germany had also flown trials with remote-controlled aerial gliders (Torpedogleiter) build by Siemens-Schuckert beginning in 1915.
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, Sergey Korolev headed the GIRD-06 cruise missile project from 1932 to 1939, which used a rocket-powered boost-glide 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.
Germany first deployed cruise style missiles, during World War II. The V-1, often referred to as flying bomb, contained a gyroscopic guidance system and was propelled by a simple pulse-jet engine, the sound of which gave it the nickname of “buzz bomb”.
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 V-1 required stationary launch ramps which were susceptible to bombardment. Nazi Germany, in 1943, also developed the Mistel 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 towards the end of the war.
Immediately after the war the United States Air Force had 21 different guided missile projects including would-be cruise missiles. All were cancelled by 1948 except four: the Air Material Command BANSHEE, the SM-62 Snark, the SM-64 Navaho, and the MGM-1 Matador. The BANSHEE design was similar to Operation Aphrodite; like Aphrodite it failed, and was canceled in April 1949.
During the Cold War period both the United States and the Soviet Union experimented further with the concept, deploying early cruise missiles from land, submarines and aircraft. The main outcome of the US Navy submarine missile project was the SSM-N-8 Regulus missile, based upon the V-1.
The US Air Force’s first operational surface-to-surface missile was the winged, mobile, nuclear-capable MGM-1 Matador, also similar in concept to the V-1. Deployment overseas began in 1954, first to West Germany and later to the Republic of China (Taiwan) and South Korea. On November 7, 1956, U. S. Air Force Matador units in West Germany, whose missiles were capable of striking targets in the Warsaw Pact, deployed from their fixed day-to-day sites to unannounced dispersed launch locations. This alert was in response to the crisis posed by the Soviet attack on Hungary which suppressed the 1956 Hungarian Revolution.
Between 1957 and 1961 the United States followed an ambitious and well-funded program to develop a nuclear-powered cruise missile, Project Pluto. It was designed to fly below the enemy’s radar at speeds above Mach 3 and carry a number of hydrogen bombs that it would drop on its path over enemy territory. Although the concept was proven sound and the 500 megawatt engine finished a successful test run in 1961, no airworthy device was ever completed. The project was finally abandoned in favor of ICBM development.
While ballistic missiles were the preferred weapons for land targets, heavy nuclear and conventional tipped cruise missiles were seen by the USSR as a primary weapon to destroy US naval carrier battle groups. Large submarines (for example, Echo and Oscar classes) were developed to carry these weapons and shadow US battle groups at sea, and large bombers (for example, Backfire, Bear, and Blackjack models) were equipped with the weapons in their air-launched cruise missile (ALCM) configuration.
Cruise missiles generally consist of a guidance system, payload, and propulsion system, housed in an airframe with small wings and empennage for flight control. Payloads usually consist of a conventional warhead or a nuclear warhead. Cruise missiles tend to be propelled by a jet engine, turbofan engines being preferred due to their greater efficiency at low altitude and sub-sonic speed.
Guidance systems also vary greatly. Low-cost systems use a radar altimeter, barometric altimeter and clock to navigate a digital strip map. More advanced systems use inertial guidance, satellite navigation and terrain contour matching (TERCOM). Use of an automatic target recognition (ATR) algorithm/device in the guidance system increases accuracy of the missile. The Standoff Land Attack Missile features an ATR unit from General Electric.
Cruise missiles can be categorized by size, speed (subsonic or supersonic), and range, and whether launched from land, air, surface ship, or submarine. Often versions of the same missile are produced for different launch platforms; sometimes air- and submarine-launched versions are a little lighter and smaller than land- and ship-launched versions.
Guidance systems can vary across missiles. Some missiles can be fitted with any of a variety of navigation systems (Inertial navigation, TERCOM, or satellite navigation). Larger cruise missiles can carry either a conventional or a nuclear warhead, while smaller ones carry only conventional warheads.