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. 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.
In 1916, Lawrence Sperry built and patented an "aerial torpedo", the Hewitt-Sperry Automatic Airplane, 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 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.
Immediately after the war the United States Air Force had 21 different guided missile projects, including would-be cruise missiles. All but four were cancelled by 1948, — the Air Materiel 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 cancelled 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 United States Navy submarine missile project was the SSM-N-8 Regulus missile, based upon the V-1.
The United States 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 7 November 1956, U.S. Air Force deployed Matador units in West Germany, whose missiles were capable of striking targets in the Warsaw Pact, 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 Hungarian Revolution of 1956.
Between 1957 and 1961 the United States followed an ambitious and well-funded program to develop a nuclear-powered cruise missile, Supersonic Low Altitude Missile (SLAM). 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 along 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 weapon tipped cruise missiles were seen by the USSR as a primary weapon to destroy United States naval carrier battle groups. Large submarines (for example, Echo and Oscar classes) were developed to carry these weapons and shadow United States 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 aircraft 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 subsonic 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 guidance 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.
These missiles travel faster than the speed of sound, usually using ramjet engines. The range is typically 100–500 km, but can be greater. Guidance systems vary.
The United States, Russia, United Kingdom, Israel, South Korea, Turkey, Iran, China, Pakistan and India have developed several long-range subsonic cruise missiles. These missiles have a range of over 1,000 kilometres (620 mi) and fly at about 800 kilometres per hour (500 mph). They typically have a launch weight of about 1,500 kilograms (3,300 lb) and can carry either a conventional or a nuclear warhead. Earlier versions of these missiles used inertial navigation; later versions use much more accurate TERCOM and DSMAC systems. Most recent versions can use satellite navigation.
These missiles are about the same size and weight and fly at similar speeds to the above category, but the range is (officially) less than 1,000 km. Guidance systems vary.
These are subsonic missiles which weigh around 500 kilograms (1,102 lb) and have a range of up to 300 km (190 mi).
The most common mission for cruise missiles is to attack relatively high-value targets such as ships, command bunkers, bridges and dams. Modern guidance systems permit accurate attacks.
As of 2001 the BGM-109 Tomahawk missile model has become a significant part of the United States naval arsenal. It gives ships and submarines an extremely accurate, long-range, conventional land attack weapon. Each costs about $1.99 million USD. Both the Tomahawk and the AGM-86 were used extensively during Operation Desert Storm. On 7 April 2017, during the Syrian Civil War, U.S. warships fired more than 50 cruise missiles into a Syrian air base in retaliation for a Syrian Sarin gas attack against a rebel stronghold.
The United States Air Force (USAF) deploys an air-launched cruise missile, the AGM-86 ALCM. The Boeing B-52 Stratofortress is the exclusive delivery vehicle for the AGM-86 and AGM-129 ACM. Both missile types are configurable for either conventional or nuclear warheads.
The USAF adopted the AGM-86 for its bomber fleet while AGM-109 was adapted to launch from trucks and ships and adopted by the USAF and Navy. The truck-launched versions, and also the Pershing II and SS-20 Intermediate Range Ballistic Missiles, were later destroyed under the bilateral INF (Intermediate Range Nuclear Forces) treaty with the USSR.
The British Royal Navy (RN) also operates cruise missiles, specifically the U.S.-made Tomahawk, used by the RN's nuclear submarine fleet. UK conventional warhead versions were first fired in combat by the RN in 1999, during the Kosovo War (the United States fired cruise missiles in 1991). The Royal Air Force uses the Storm Shadow cruise missile on its Tornado GR4 aircraft. It is also used by France, where it is known as SCALP EG, and carried by the Armée de l'Air's Mirage 2000 and Rafale aircraft.
India and Russia have jointly developed the supersonic cruise missile BrahMos. There are three versions of the Brahmos: ship/land-launched, air-launched and sub-launched. The ship/land-launched version were operational as of late 2007. The Brahmos has the capability to attack targets on land. Russia also continues to operate other cruise missiles: the SS-N-12 Sandbox, SS-N-19 Shipwreck, SS-N-22 Sunburn and SS-N-25 Switchblade. Germany and Spain operate the Taurus missile while Pakistan has copied the US supplied Harpoon missile and made Babur missile. Both the People's Republic of China and the Republic of China (Taiwan) have designed several cruise missile variants, such as the well-known C-802, some of which are capable of carrying biological, chemical, nuclear, and conventional warheads.
The French Force de Frappe nuclear forces include both land and sea-based bombers with Air-Sol Moyenne Portée high speed medium range nuclear cruise missiles. Two models are in use, ASMP and a newer ASMP-A. Approximately 60 nuclear missiles are in service, 50 land based and 10 sea-based.
India in 2017 successfully flight-tested its indigenous Nirbhay ('Fearless') land-attack cruise missile, which can deliver nuclear warheads to a strike range of 1,000-km  Nirbhay had been flight tested unsuccessfully and repeatedly since 2013, leading to concerns that the project would be cancelled.
The Israel Defense Forces reportedly deploy the medium-range air-launched Popeye Turbo ALCM and the Popeye Turbo SLCM medium-long range cruise missile with nuclear warheads on Dolphin class submarines.
Pakistan currently has four cruise missile systems: the air-launched Ra'ad; the ground and underwater launched Babur; ship-launched Harbah missile and surface launched Zarb missile. Both, Ra'ad and Babur, can carry nuclear warheads between 10 and 25 kt, and deliver them to targets at a range of 350 km (220 mi) and 700 km (430 mi) respectively. Babur has been in service with the Pakistan Army since 2010.
Russia has Kh-55SM cruise missiles, with similar to United States' AGM-129 range of 3000 km, but are able to carry a more powerful warhead of 200 kt. They are equipped with a TERCOM system which allows them to cruise at an altitude lower than 110 meters at subsonic speeds while obtaining a CEP accuracy of 15 meters with an Inertial navigation system. They are air-launched from either Tupolev Tu-95s, Tupolev Tu-22Ms, or Tupolev Tu-160s, each able to carry 16 for the Tu-95, 12 for the Tu-160, and 4 for the Tu-22M. A stealth version of the missile, the Kh-101 is in development. It has similar qualities as the Kh-55, except that its range has been extended to 5,000 km, equipped with a 1,000 kg conventional warhead, and has stealth features which reduces its probability of intercept.
The United States has deployed four nuclear cruise missiles at one time or another.
Currently cruise missiles are among the most expensive of single-use weapons, up to several million dollars apiece. One consequence of this is that its users face difficult choices in target allocation, to avoid expending the missiles on targets of low value. For instance during Operation Enduring Freedom the United States attacked targets of very low monetary value with cruise missiles, which led many to question the efficiency of the weapon. However, proponents of the cruise missile counter that the same argument applies to other types of UAVs: they are cheaper than human pilots when total training and infrastructure costs are taken into account, not to mention the risk of loss of personnel. As demonstrated in Operation Odyssey Dawn and prior conflicts, cruise missiles are much more difficult to detect and intercept than other aerial assets (reduced radar cross-section, infrared and visual signature due to smaller size), suiting them to attacks against static air defense systems. The development of hypersonic missiles systems is, however, problematic from a geopolitical perspective. In an article on this topic, Professor Nayef Al-Rodhan warned that a test ban is very unlikely and that the technology will renew a strategic arms race and geopolitical rivalries.