In modern language, a missile known as a guided missile, is a guided self-propelled system, as opposed to an unguided self-propelled munition, referred to as a rocket. Missiles have four system components: targeting or missile guidance, flight system and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles, surface-to-air missiles, air-to-air missiles, anti-satellite weapons. All known existing missiles are designed to be propelled during powered flight by chemical reactions inside a rocket engine, jet engine, or other type of engine. Non-self-propelled airborne explosive devices are referred to as shells and have a shorter range than missiles. In ordinary British-English usage predating guided weapons, a missile is such as objects thrown at players by rowdy spectators at a sporting event; the first missiles to be used operationally were a series of missiles developed by Nazi Germany in World War II. Most famous of these are the V-1 flying bomb and V-2 rocket, both of which used a simple mechanical autopilot to keep the missile flying along a pre-chosen route.
Less well known were a series of anti-shipping and anti-aircraft missiles based on a simple radio control system directed by the operator. However, these early systems in World War II were only built in small numbers. Guided missiles have a number of different system components: Guidance system Targeting system Flight system Engine Warhead The most common method of guidance is to use some form of radiation, such as infrared, lasers or radio waves, to guide the missile onto its target; this radiation may emanate from the target, it may be provided by the missile itself, or it may be provided by a friendly third party. The first two are known as fire-and-forget as they need no further support or control from the launch vehicle/platform in order to function. Another method is to use a TV guidance, with a visible light or infrared picture produced in order to see the target; the picture may be used either by a human operator who steering the missile onto its target or by a computer doing much the same job.
One of the more bizarre guidance methods instead used a pigeon to steer a missile to its target. Some missiles have a home-on-jam capability to guide itself to a radar-emitting source. Many missiles use a combination of two or more of the methods to improve accuracy and the chances of a successful engagement. Another method is to target the missile by knowing the location of the target and using a guidance system such as INS, TERCOM or satellite guidance; this guidance system guides the missile by knowing the missile's current position and the position of the target, calculating a course between them. This job can be performed somewhat crudely by a human operator who can see the target and the missile and guide it using either cable- or radio-based remote control, or by an automatic system that can track the target and the missile. Furthermore, some missiles use initial targeting, sending them to a target area, where they will switch to primary targeting, using either radar or IR targeting to acquire the target.
Whether a guided missile uses a targeting system, a guidance system or both, it needs a flight system. The flight system uses the data from the targeting or guidance system to maneuver the missile in flight, allowing it to counter inaccuracies in the missile or to follow a moving target. There are two main systems: aerodynamic maneuvering. Missiles are powered by an engine either a type of rocket engine or jet engine. Rockets are of the solid propellant type for ease of maintenance and fast deployment, although some larger ballistic missiles use liquid-propellant rockets. Jet engines are used in cruise missiles, most of the turbojet type, due to its relative simplicity and low frontal area. Turbofans and ramjets are the only other common forms of jet engine propulsion, although any type of engine could theoretically be used. Long-range missiles may have multiple engine stages in those launched from the surface; these stages may all be of similar types or may include a mix of engine types − for example, surface-launched cruise missiles have a rocket booster for launching and a jet engine for sustained flight.
Some missiles may have additional propulsion from another source at launch. Missiles have one or more explosive warheads, although other weapon types may be used; the warheads of a missile provide its primary destructive power. Warheads are most of the high explosive type employing shaped charges to exploit the accuracy of a guided weapon to destroy hardened targets. Other warhead types include submunitions, nuclear weapons, biological or radiological weapons or kinetic energy penetrators. Warheadless missiles are used for testing and training purposes. Missiles are categorized by their launch platform and intended target. In broadest terms, these will either be surface or air, t
Europe is a continent located in the Northern Hemisphere and in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south, it comprises the westernmost part of Eurasia. Since around 1850, Europe is most considered to be separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas and the waterways of the Turkish Straits. Although the term "continent" implies physical geography, the land border is somewhat arbitrary and has been redefined several times since its first conception in classical antiquity; the division of Eurasia into two continents reflects East-West cultural and ethnic differences which vary on a spectrum rather than with a sharp dividing line. The geographic border does not follow political boundaries, with Turkey and Kazakhstan being transcontinental countries. A strict application of the Caucasus Mountains boundary places two comparatively small countries and Georgia, in both continents.
Europe covers 2 % of the Earth's surface. Politically, Europe is divided into about fifty sovereign states of which the Russian Federation is the largest and most populous, spanning 39% of the continent and comprising 15% of its population. Europe had a total population of about 741 million as of 2016; the European climate is affected by warm Atlantic currents that temper winters and summers on much of the continent at latitudes along which the climate in Asia and North America is severe. Further from the sea, seasonal differences are more noticeable than close to the coast. Europe, in particular ancient Greece, was the birthplace of Western civilization; the fall of the Western Roman Empire in 476 AD and the subsequent Migration Period marked the end of ancient history and the beginning of the Middle Ages. Renaissance humanism, exploration and science led to the modern era. Since the Age of Discovery started by Portugal and Spain, Europe played a predominant role in global affairs. Between the 16th and 20th centuries, European powers controlled at various times the Americas all of Africa and Oceania and the majority of Asia.
The Age of Enlightenment, the subsequent French Revolution and the Napoleonic Wars shaped the continent culturally and economically from the end of the 17th century until the first half of the 19th century. The Industrial Revolution, which began in Great Britain at the end of the 18th century, gave rise to radical economic and social change in Western Europe and the wider world. Both world wars took place for the most part in Europe, contributing to a decline in Western European dominance in world affairs by the mid-20th century as the Soviet Union and the United States took prominence. During the Cold War, Europe was divided along the Iron Curtain between NATO in the West and the Warsaw Pact in the East, until the revolutions of 1989 and fall of the Berlin Wall. In 1949 the Council of Europe was founded, following a speech by Sir Winston Churchill, with the idea of unifying Europe to achieve common goals, it includes all European states except for Belarus and Vatican City. Further European integration by some states led to the formation of the European Union, a separate political entity that lies between a confederation and a federation.
The EU originated in Western Europe but has been expanding eastward since the fall of the Soviet Union in 1991. The currency of most countries of the European Union, the euro, is the most used among Europeans. In classical Greek mythology, Europa was a Phoenician princess; the word Europe is derived from her name. The name contains the elements εὐρύς, "wide, broad" and ὤψ "eye, countenance", hence their composite Eurṓpē would mean "wide-gazing" or "broad of aspect". Broad has been an epithet of Earth herself in the reconstructed Proto-Indo-European religion and the poetry devoted to it. There have been attempts to connect Eurṓpē to a Semitic term for "west", this being either Akkadian erebu meaning "to go down, set" or Phoenician'ereb "evening, west", at the origin of Arabic Maghreb and Hebrew ma'arav. Michael A. Barry, professor in Princeton University's Near Eastern Studies Department, finds the mention of the word Ereb on an Assyrian stele with the meaning of "night, sunset", in opposition to Asu " sunrise", i.e. Asia.
The same naming motive according to "cartographic convention" appears in Greek Ἀνατολή. Martin Litchfield West stated that "phonologically, the match between Europa's name and any form of the Semitic word is poor." Next to these hypotheses there is a Proto-Indo-European root *h1regʷos, meaning "darkness", which produced Greek Erebus. Most major world languages use words derived from Europa to refer to the continent. Chinese, for example, uses the word Ōuzhōu. In some Turkic languages the Persian name Frangistan is used casually in referring to much of Europe, besides official names such as Avrupa or Evropa; the prevalent definition of Europe as a geographical term has been in use since the mid-19th century. Europe is taken to be bounded by large bodies of water
The PlayStation 2 is a home video game console, developed by Sony Computer Entertainment. It is the successor to the original PlayStation console and is the second iteration in the PlayStation lineup of consoles, it was released in 2000 and competed with Sega's Dreamcast, Nintendo's GameCube and Microsoft's Xbox in the sixth generation of video game consoles. Announced in 1999, the PlayStation 2 offered backwards compatibility for its predecessor's DualShock controller, as well as for its games; the PlayStation 2 is the best-selling video game console of all time, selling over 155 million units, with 150 million confirmed by Sony in 2011. More than 3,874 game titles have been released for the PS2 since launch, more than 1.5 billion copies have been sold. Sony manufactured several smaller, lighter revisions of the console known as Slimline models in 2004. In 2006, Sony announced and launched its successor, the PlayStation 3. With the release of its successor, the PlayStation 2 remained popular well into the seventh generation and continued to be produced until January 4, 2013, when Sony announced that the PlayStation 2 had been discontinued after 12 years of production – one of the longest runs for a video game console.
Despite the announcement, new games for the console continued to be produced until the end of 2013, including Final Fantasy XI: Seekers of Adoulin for Japan, FIFA 13 for North America, Pro Evolution Soccer 2014 for Europe. Repair services for the system in Japan ended on September 7, 2018. Though Sony has kept details of the PlayStation 2's development secret, work on the console began around the time that the original PlayStation was released. Insiders stated that it was developed in the U. S. West Coast by former members of Argonaut Software. By 1997 word had leaked to the press that the console would have backwards compatibility with the original PlayStation, a built-in DVD player, Internet connectivity. Sony announced the PlayStation 2 on March 1, 1999; the video game console was positioned as a competitor to Sega's Dreamcast, the first sixth-generation console to be released, although the main rivals of the PS2 were Nintendo's GameCube and Microsoft's Xbox. The Dreamcast itself launched successfully in North America that year, selling over 500,000 units within two weeks.
Soon after the Dreamcast's North American launch, Sony unveiled the PlayStation 2 at the Tokyo Game Show on September 20, 1999. Sony showed playable demos of upcoming PlayStation 2 games including Gran Turismo 2000 and Tekken Tag Tournament – which showed the console's graphic abilities and power; the PS2 was launched in March 2000 in Japan, October in North America, November in Europe. Sales of the console and accessories pulled in $250 million on the first day, beating the $97 million made on the first day of the Dreamcast. Directly after its release, it was difficult to find PS2 units on retailer shelves due to manufacturing delays. Another option was purchasing the console online through auction websites such as eBay, where people paid over a thousand dollars for the console; the PS2 sold well on the basis of the strength of the PlayStation brand and the console's backward compatibility, selling over 980,000 units in Japan by March 5, 2000, one day after launch. This allowed the PS2 to tap the large install base established by the PlayStation – another major selling point over the competition.
Sony added new development kits for game developers and more PS2 units for consumers. The PS2's built-in functionality expanded its audience beyond the gamer, as its debut pricing was the same or less than a standalone DVD player; this made the console a low cost entry into the home theater market. The success of the PS2 at the end of 2000 caused Sega problems both financially and competitively, Sega announced the discontinuation of the Dreamcast in March 2001, just 18 months after its successful launch; the PS2 remained as the only active sixth generation console for over 6 months, before it would face competition from newer rivals. Many analysts predicted a close three-way matchup among the three consoles. While the PlayStation 2 theoretically had the weakest specification of the three, it had a head start due to its installed base plus strong developer commitment, as well as a built-in DVD player. While the PlayStation 2's initial games lineup was considered mediocre, this changed during the 2001 holiday season with the release of several blockbuster games that maintained the PS2's sales momentum and held off its newer rivals.
Sony countered the Xbox by temporarily securing PlayStation 2 exclusives for anticipated games such as the Grand Theft Auto series and Metal Gear Solid 2: Sons of Liberty. Sony cut the price of the console in May 2002 from US$299 to $199 in North America, making it the same price as the GameCube and $100 less than the Xbox, it planned to cut the price in Japan around that time. It cut the price twice in Japan in 2003. In 2006, Sony cut the cost of the console in anticipation of the release of the PlayStation 3. Sony, unlike Sega with its Dreamcast placed little emphasis on online gaming during its first few years, although that changed upon the launch of the online-capable Xbox. Coinciding with the release of Xbox Live, Sony released the PlayStation Network Adapter in late 2002, with several online first–party titles released alongside it, such as SOCOM: U. S. Navy SEALs to demon
Sony Interactive Entertainment
Sony Interactive Entertainment LLC is a multinational video game and digital entertainment company, a wholly owned subsidiary of Sony Corporation of America, the central hub for the American businesses under the Japanese conglomerate Sony Corporation. The company was founded in Tokyo and established on November 16, 1993, as Sony Computer Entertainment, to handle Sony's venture into video game development through its PlayStation brand. Since the successful launch of the original PlayStation console in 1994, the company has been developing the PlayStation lineup of home video game consoles and accessories. Expanding into North America and other countries, the company became Sony's main resource for research and development in video games and interactive entertainment. In April 2016, SCE and Sony Network Entertainment International was restructured and reorganized into Sony Interactive Entertainment, carrying over the operations and primary objectives from both companies; the same year, SIE moved its headquarters from Tokyo to California.
Sony Interactive Entertainment handles the research and development and sales of both hardware and software for the PlayStation video game systems. SIE is a developer and publisher of video game titles, operates several subsidiaries in Sony's largest markets: North America and Asia. By August 2018, the company had sold more than 525 million PlayStation consoles worldwide. Sony Computer Entertainment, Inc. was jointly established by Sony and its subsidiary Sony Music Entertainment Japan in 1993 to handle the company's ventures into the video game industry. The original PlayStation console was released on December 1994, in Japan; the company's North American operations, Sony Computer Entertainment of America, were established in May 1995 as a division of Sony Electronic Publishing. Located in Foster City, the North American office was headed by Steve Race. In the months prior to the release of the PlayStation in Western markets, the operations were restructured: All video game marketing from Sony Imagesoft was folded into SCEA in July 1995, with most affected employees transferred from Santa Monica to Foster City.
On August 7, 1995, Race unexpectedly resigned and was named CEO of Spectrum HoloByte three days later. He was replaced by Sony Electronics veteran Martin Homlish; this proved to be the beginning of a run of exceptional managerial turnover, with SCEA going through four presidents in a single year. The PS console was released in the United States on September 9, 1995; as part of a worldwide restructuring at the beginning of 1997, SCEA and Sony Computer Entertainment Europe were both re-established as wholly owned subsidiaries of SCEI. The launch of the second PS console, the PlayStation 2 was released in Japan on March 4, 2000, the U. S. on October 26, 2000. On July 1, 2002, chairman of SCEI, Shigeo Maruyama, was replaced by Tamotsu Iba as chairman. Jack Tretton and Phil Harrison were promoted to senior vice presidents of SCE; the PlayStation Portable was SCEI's first foray into the small handheld console market. Its development was first announced during SCE's E3 conference in 2003, it was unveiled during their E3 conference on May 11, 2004.
The system was released in Japan on December 12, 2004, in North America on March 24, 2005, in Europe and Australia on September 1, 2005. On September 14, 2005, SCEI formed Sony Computer Entertainment Worldwide Studios, a single internal entity to oversee all wholly owned development studios within SCEI, it became responsible for the creative and strategic direction of development and production of all computer entertainment software by all SCEI-owned studios—all software is produced for the PS family of consoles. Shuhei Yoshida was named as President of SCE WWS on May 16, 2008, replacing Kazuo Hirai, serving interim after Harrison left the company in early 2008. On December 8, 2005, video game developer Guerrilla Games, developers of the Killzone series, was acquired by Sony Computer Entertainment as part of its SCE WWS. On January 24, 2006, video game developer Zipper Interactive, developers of the Socom series, was acquired by Sony Computer Entertainment as part of its SCE WWS. In March 2006, Sony announced the online network for its forthcoming PlayStation 3 system at the 2006 PlayStation Business Briefing meeting in Tokyo, tentatively named "PlayStation Network Platform" and called just PlayStation Network.
Sony stated that the service would always be connected and include multiplayer support. The launch date for the PS3 was announced by Hirai at the pre-Electronic Entertainment Expo conference held at the Sony Pictures Studios in Los Angeles, California, on May 8, 2006; the PS3 was released in Japan on November 11, 2006, the U. S. date was November 17, 2006. The PSN was launched in November 2006. On November 30, 2006, president of SCEI, Ken Kutaragi, was appointed as chairman of SCEI, while Hirai president of SCEA, was promoted to president of SCEI. On April 26, 2007, Ken Kutaragi resigned from his position as chairman of SCEI and group CEO, passing on his duties to the appointed president of SCE, Hirai. On September 20, 2007, video game developers Evolution Studios and Bigbig Studios, creators of the MotorStorm series, were acquired by Sony Computer Entertainment as part of its SCE WWS. On April 15, 2009, David Reeves, president and CEO of SCE Europe, announced his forthcoming resignation from his post.
He had joined the company in 1995 and was appointed as chairman of SCEE in 2003, president in 2005. His role of president and CEO of SCEE would be taken over by Andrew House, who joined Sony Corporation in 1990; the PSP Go was released on October 1
The PlayStation 4 is an eighth-generation home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 3 in February, 2013, it was launched on November 15 in North America, November 29 in Europe, South America and Australia, on February 22, 2014, in Japan, it Switch. Moving away from the more complex Cell microarchitecture of its predecessor, the console features an AMD Accelerated Processing Unit built upon the x86-64 architecture, which can theoretically peak at 1.84 teraflops. The PlayStation 4 places an increased emphasis on social interaction and integration with other devices and services, including the ability to play games off-console on PlayStation Vita and other supported devices, the ability to stream gameplay online or to friends, with them controlling gameplay remotely; the console's controller was redesigned and improved over the PlayStation 3, with improved buttons and analog sticks, an integrated touchpad among other changes.
The console supports HDR10 High-dynamic-range video and playback of 4K resolution multimedia. The PlayStation 4 was released to acclaim, with critics praising Sony for acknowledging its consumers' needs, embracing independent game development, for not imposing the restrictive digital rights management schemes to those announced by Microsoft for Xbox One. Critics and third-party studios praised the capabilities of the PlayStation 4 in comparison to its competitors. Heightened demand helped Sony top global console sales. By the end of December 2018, over 94 million PlayStation 4 consoles had been shipped worldwide, surpassing lifetime sales of its predecessor, the PlayStation 3; as of December 2018, 91.6 million PlayStation 4 consoles had been sold through to customers worldwide. On September 7, 2016, Sony unveiled the PlayStation 4 Pro, a high-end version of the console with an upgraded GPU and higher CPU clock rate to support enhanced performance and 4K resolution on supported games; the company released a variant of the original model with a smaller form factor, the release of a patch to add HDR support to all existing consoles.
According to lead architect Mark Cerny, development of Sony's fourth video game console began as early as 2008. Less than two years earlier, the PlayStation 3 had launched after months of delays due to issues with production; the delay placed Sony a year behind Microsoft's Xbox 360, approaching unit sales of 10 million by the time the PS3 launched. PlayStation Europe CEO Jim Ryan said Sony wanted to avoid repeating the same mistake with PS3's successor. In designing the system, Sony worked with software developer Bungie, who offered their input on the controller and how to make it better for shooting games. In 2012, Sony began shipping development kits to game developers, consisting of a modified PC running the AMD Accelerated Processing Unit chipset; these development kits were known as "Orbis". In early 2013, Sony announced that an event known as PlayStation Meeting 2013 would be held in New York City, U. S. on February 20, 2013, to cover the "future of PlayStation". Sony announced the PlayStation 4 at the event.
It revealed details about the console's hardware and discussed some of the new features it will introduce. Sony showed off real-time footage of games in development, as well as some technical demonstrations; the design of the console was unveiled in June at the Electronic Entertainment Expo 2013, the initial recommended retail prices of $399, €399, £349 given. The company revealed release dates for North America, Central America, South America and Australia, as well as final pieces of information, at a Gamescom press event in Cologne, Germany, on August 20, 2013; the console was released on November 15, 2013, in the United States and Canada, followed by further releases on November 29, 2013. By the end of 2013, the PS4 was launched in more European and South American countries The PS4 released in Japan at ¥39,980 on February 22, 2014. Sony finalized a deal with the Chinese government in May 2014 to sell its products in mainland China, the PS4 will be the first product to be released. Kazuo Hirai, chief executive officer of Sony, said in May: "The Chinese market, just given the size of it, is potentially a large market for video game products...
I think that we will be able to replicate the kind of success we have had with PS4 in other parts of the world in China."In September 2015, Sony reduced the price of the PS4 in Japan to ¥34,980, with similar price drops in other Southeast Asian markets. The first official sub £300 PS4 bundle was the £299.99 "Uncharted Nathan Drake Collection 500GB", released in the UK on October 9, 2015. On October 9, 2015, the first official price cut of the PS4 in North America was announced: a reduction of $50 to $349.99 and by $20 to $429.99. An official price cut in Europe followed in late October 2015, reduced to €349.99/£299.99. On June 10, 2016, Sony confirmed that a hardware revision of the PlayStation 4, rumored to be codenamed "Neo", was under development; the new revision is a higher-end model, meant to support gameplay in 4K. The new model will be sold alongside the existing model, all existing software will be compatible between the two models. Layden stated that Sony has no plans to "bifurcate the market", only that gamers playing on the Neo will "have the same experience, but one will be delivered at a higher resol
Fired Up (video game)
Fired Up is a vehicular combat game available on the PlayStation Portable. The game features a single-player campaign and a multiplayer mode which supports up to eight players; the game features a demo of Wipeout Medievil: Resurrection. Fired Up features game sharing and downloadable content, it is derived from the 2002 PlayStation 2 online game Hardware: Online Arena. Fired Up's Campaign mode is set in an unnamed eastern European country, invaded by a neighbouring country only known as "The Republic"; the player plays as a fighter for a resistance army in several different vehicles. The player can take on the subsequent missions, whenever they please, otherwise they can find yellow scavenge tokens which, for each 10 tokens collected, will unlock new secondary weapons, which the player can use against AI enemies that spawn to attack the player; these weapons include grenades, heavy missiles, laser. There are turrets around the map for the player to use. Available are challenges, taking in the form of large trucks that roam the city.
Upon destruction of one, the player must seek and eliminate the required number of enemies before the allocated time elapses. For every level of challenge complete and better, health and armor pickups will spawn for the player to collect. Fired Up features a multiplayer mode which supports up to eight players, through ad-hoc; the host can choose a variety of maps, game modes. Prior to the game starting, players can choose their preferred vehicle. Deathmatch - Straight up vehicular brawl. Weapons vary on the map. Includes Team Deathmatch. Team Capture the Flag - Players must grab the enemies' flag and return it to their base to score a point. Be wary as the enemy will do the same. King of the Hill - A point is to be contested by all players; the winner is the one. Includes Team King of the Hill. Team Bomb the Base - Players must pick up explosives, spawning randomly across the map, deliver them to the enemy's base. Ownership of bombs are carried over to players. Assimilation - All players begin'infected' but can find and pickup'Antidote' pickups to cure them.
The infected must re-infect those by finding and either contact or kill. The last remaining player to be infected wins. Race - The map is modified into a circuit and the first player to cross the finish line, is the winner. Along the way are items for the player to use, but they may either help or hinder the player in some way; the game features game sharing to allow those to provide a'demo' version of the game to those who do not own a copy. Included is a Wipeout Pure demo. Fired Up at GameSpot
A machine gun is a automatic mounted or portable firearm designed to fire rifle cartridges in rapid succession from an ammunition belt or magazine for the purpose of suppressive fire. Not all automatic firearms are machine guns. Submachine guns, assault rifles, battle rifles, pistols or cannons may be capable of automatic fire, but are not designed for sustained fire; as a class of military rapid-fire guns, machine guns are automatic weapons designed to be used as support weapons and used when attached to a mount- or fired from the ground on a bipod or tripod. Many machine guns use belt feeding and open bolt operation, features not found on rifles. In the U. S. A, a "machine gun" is a legal term for any weapon able to fire more than one shot per function of the trigger regardless of caliber, the receiver of any such weapon, any weapon convertible to such a state using normal tools, or any component or part that will modify an existing firearm such that it functions as a "machine gun" such as a drop-in auto sear.
Civilian possession of such weapons manufactured prior to 1986 is not prohibited by any federal law and not illegal in many states, but they must be registered as Title II weapons under the National Firearms Act and have a tax stamp paid. Machine guns manufactured after 1986 are prohibited by the Hughes Amendment to the Gun Owners Protection Act. Unlike semi-automatic firearms, which require one trigger pull per round fired, a machine gun is designed to fire for as long as the trigger is held down. Nowadays the term is restricted to heavy weapons, able to provide continuous or frequent bursts of automatic fire for as long as ammunition lasts. Machine guns are used against personnel and light vehicles, or to provide suppressive fire, either directly or indirectly, they are mounted on fast attack vehicles such as technicals to provide heavy mobile firepower, armored vehicles such as tanks for engaging targets too small to justify use of the primary weaponry or too fast to engage with it, on aircraft as defensive armament or for strafing ground targets, though on fighter aircraft true machine guns have been supplanted by large-caliber rotary guns.
Some machine guns have in practice sustained fire continuously for hours. Because they become hot all machine guns fire from an open bolt, to permit air cooling from the breech between bursts, they usually have either a barrel cooling system, slow-heating heavyweight barrel, or removable barrels which allow a hot barrel to be replaced. Although subdivided into "light", "medium", "heavy" or "general-purpose" the lightest machine guns tend to be larger and heavier than standard infantry arms. Medium and heavy machine guns are either mounted on a vehicle. Light machine guns are designed to provide mobile fire support to a squad and are air-cooled weapons fitted with a box magazine or drum and a bipod. Medium machine guns use full-sized rifle rounds and are designed to be used from fixed positions mounted on a tripod. Heavy machine gun is a term originating in World War I to describe heavyweight medium machine guns and persisted into World War II with Japanese Hotchkiss M1914 clones. A general-purpose machine gun is a lightweight medium machine gun which can either be used with a bipod and drum in the light machine gun role or a tripod and belt feed in the medium machine gun role.
Machine guns have simple iron sights, though the use of optics is becoming more common. A common aiming system for direct fire is to alternate solid rounds and tracer ammunition rounds, so shooters can see the trajectory and "walk" the fire into the target, direct the fire of other soldiers. Many heavy machine guns, such as the Browning M2.50 caliber machine gun, are accurate enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the record for a long-distance shot at 7,382 ft with a.50 caliber heavy machine gun he had equipped with a telescopic sight. This led to the introduction of.50 caliber anti-materiel sniper rifles, such as the Barrett M82. Other automatic weapons are subdivided into several categories based on the size of the bullet used, whether the cartridge is fired from a closed bolt or an open bolt, whether the action used is locked or is some form of blowback. Automatic firearms using pistol-calibre ammunition are called machine pistols or submachine guns on the basis of size.
The term personal defense weapon is sometimes applied to weapons firing dedicated armor-piercing rounds which would otherwise be regarded as machine pistols or SMGs, but it is not strongly defined and has been used to describe a range of weapons from ordinary SMGs to compact assault rifles. Selective fire rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles or battle rifles, while rifles that fire an intermediate cartridge are called assault rifles. Assault rifles are a compromise between the size and weight of a pistol-calibre submachine gun and a full size battle rifle, firing intermediate cartridges and allowing semi-automatic and burst or full-automatic fire options