Stealth action video games are generally more oriented towards staying hidden, avoiding conflict, or being stealthy in order to complete your assigned objectives. This genre is in many ways the antithesis of the action genre, which generally relies heavily upon fast-paced action and direct confrontation. Many games however, blur the line between the two genres; while others still may allow the player to choose whether to make the game a first-person shoot, or a first-person sneaker, or some variant in-between.
The Metal Gear series is generally believed to have initiated the phrase. The genre has grown in size over the last few years, and many now consider it a genre in its own right, rather than simply a gaming term. Titles like the Thief series or Tom Clancy's Splinter Cell have further legitimized the genre and made both publishers and developers realize there is, in fact, a market for such games.
A stealth game is a type of video game that rewards the player for using stealth to avoid or overcome antagonists. Games in the genre typically allow the player to remain undetected by hiding, using disguises, and/or avoiding noise. Some games allow the player to choose between a stealthy approach or directly attacking antagonists, perhaps rewarding the player for greater levels of stealth. The genre has employed espionage, counter-terrorism and rogue themes, with protagonists that have been identified as special forces operatives, spies, thieves, assassins and ninjas. Some games have combined stealth game elements with those of other genres, such as first-person shooters and even platform games.
Some of the early games emphasizing stealth include 005, Castle Wolfenstein, Metal Gear, and Metal Gear 2: Solid Snake. The genre became popular in 1998, with the mainstream success of Metal Gear Solid as well as Tenchu: Stealth Assassins and Thief: The Dark Project. Tenchu was the first 3D game in the genre, while Metal Gear Solid, released some months later, transformed the relatively obscure Metal Gear series into a highly acclaimed, profitable franchise with numerous sequels, while Thief pioneered 3D stealth games on the PC. These games were followed by other stealth series, such as Hitman and Splinter Cell. Later games in the genre have allowed the player to choose between, or combine, stealth tactics and direct confrontation.
Unlike most action games, stealth games challenge the player to avoid alerting enemies altogether. The core gameplay elements of the modern stealth game are to avoid combat, minimize noise, and strike enemies from the shadows. There are usually multiple ways to achieve a goal with different pathways or styles of play. Some games offer a choice between killing or merely knocking out an enemy. Players can hide behind objects or in shadows, and can strike or run past an enemy when the enemy is facing the other way. If the player attracts the attention of enemies, they usually must hide and wait until the enemies abandon their search. Thus, planning becomes important, as does trial-and-error. However, some stealth games put more emphasis on physical combat skill when the player is spotted.
When hiding in the dark is a gameplay element, light and shadow become important parts of the level design. Usually the player is able to disable certain light sources. Stealth games also emphasize the audio design when players must be able to hear the subtle sound effects that may alert enemies to their actions; noise will often vary as the player walks on different surfaces such as wood or metal. Players who move recklessly will make more noise and attract more attention.
In order for a game to include stealth gameplay, the knowledge of the artificial intelligence (AI) must be restricted to make it ignorant to parts of the game world. The AI in stealth games takes into specific consideration the enemies' reactions to the effects of the player's actions, such as turning off the lights, as opposed to merely reacting to the player directly. Enemies typically have a line of sight which the player can avoid by hiding behind objects, staying in the shadows or moving while the enemy is facing another direction. Enemies can also typically detect when the player touches them or moves within a small, fixed distance. Overall, stealth games vary in what player actions the AI will perceive and react to, with more recent games offering a wider range of enemy reactions. Often, the AI's movements are predictable and regular, allowing the player to devise a strategy to overcome his adversaries.
Early developments: 1980–1986
The genre's earliest ancestor was the 1980 maze chase game Pac-Man, which laid the foundations for the stealth genre. It emphasized avoiding and running away from enemies rather than fighting them, and had an influence on the design of Metal Gear. Another early arcade maze game from 1980 that emphasized avoiding enemies was Lupin III, based on the anime of the same name, where the titular protagonist is a thief who must steal money and escape before being caught by police inspectors or guards.
SEGA's 005, released for the arcades in 1981, was an early game to employ stealth elements. Players controlled a spy who must avoid enemies as he makes his way through buildings and warehouses, where he will need to dodge the enemies' flashlights and use boxes as hiding spots. 005 holds the Guinness World Record for being the first stealth game.
Castle Wolfenstein, originally available on the Apple II in 1981, also employed stealth elements as a focus of the gameplay. Players were charged with traversing the levels of Castle Wolfenstein, stealing secret plans and escaping. Players could acquire uniforms to disguise themselves and walk by guards undetected. Beyond Castle Wolfenstein, released in 1984, included some additions to its predecessor, such as a dagger for close-range kills and a greater emphasis on disguising in enemy uniform. id Software's technically updated 1992 remake Wolfenstein 3D was originally going to feature some of the original's stealth gameplay, such as body hiding, but this was cut to make the game faster paced. This Wolfenstein game would ironically pave the way for quite a few later 3D action games, specifically first-person shooters.
Another early title to utilize stealth elements was Super Rambo Special, released by Pack-In-Video for the MSX2 in 1985. It was an action role-playing game that had elements similar to Metal Gear, with the player having to sneak around jungles, but with inferior enemy AI.
Hideo Kojima's Metal Gear, released in 1987 for the MSX2 computer and the Nintendo Entertainment System in 1988, utilized stealth elements within an action -adventure framework, and was the first mainstream stealth game, released on consoles. Since the MSX2 was not available in North America, only the NES version was released there. Metal Gear placed a greater emphasis on stealth than earlier games, with the player character Solid Snake beginning without any weapons (requiring him to avoid confrontation until weapons are found), limited ammunition for each weapon, enemies able to see from a distance (using a line-of-sight mechanic) and hear gunshots from non-silenced weapons, security cameras and sensors at various locations, and a security alarm which sounds whenever Snake is spotted and causes all enemies on screen to chase him. Snake could also disguise in enemy uniform or a cardboard box, and use his fists to fight enemies.
The sequel Metal Gear 2: Solid Snake was released in 1990 for the MSX2 and coined a name for the genre, "Tactical Espionage Game". It further evolved the stealth gameplay of its predecessor and introduced most of the gameplay elements present in Metal Gear Solid, including the three-dimensional element of height, allowing players to crouch and crawl into hiding spots and air ducts and underneath desks. The player could also distract guards by knocking on surfaces and use a radar to plan ahead. The enemies had improved AI, including a 45-degree field of vision, turning their heads left and right to see diagonally, the detection of various different noises, being able to move from screen to screen (they were limited to a single screen in earlier games), and a three-phase security alarm (where reinforcements are called in to chase the intruder, then remain on the lookout for some time after losing sight of the intruder, and then leave the area). The game also had a complex storyline and improved graphics.
Teenage Mutant Ninja Turtles, released in 1989, implemented stealth elements in its overworld map, where the player had to avoid detection by tanks. Live A Live, released by Square in 1994, was a role-playing game which featured a ninja chapter that focused on stealth, rewarding the player if the entire chapter can be completed without engaging in combat. Aliens vs. Predator, released in 1994 for the Atari Jaguar, allowed the player to become invisible and stalk enemies. The Clock Tower series, which began in 1995, were survival horror adventure games that used stealth elements to create a frightening experience, forcing the player to avoid being hunted by a demented killer rather than fighting him. In 1997, several games implemented stealth elements, including the role-playing game Final Fantasy VII which required sneaking and disguises in various segments of the game, the platform game Oddworld: Abe's Oddysee which rarely required the player to combat enemies, and certain levels in first-person shooter GoldenEye 007 that could be completed via hand-to-hand combat and the destruction of surveillance cameras. In 1998, The Legend of Zelda: Ocarina of Time also required sneaking by guards in a segment of the game.
Establishing a genre: 1998–2001
Although stealth gameplay had appeared in a several games in the 1980s and 1990s, 1998 is seen as a turning point in gaming history because of the release of Metal Gear Solid, Tenchu: Stealth Assassins, and Thief: The Dark Project. The ninja-themed game Tenchu: Stealth Assassins was released several months before Metal Gear Solid, making it the first 3D stealth-based game. The highly anticipated Metal Gear Solid transformed its modestly successful franchise into a large mainstream success. The increased power of the PlayStation console over previous platforms allowed for greater immersion in terms of both story and game environment, while the game also added several new gameplay mechanics such as hiding behind cover . Metal Gear Solid has been credited with popularizing the stealth genre. Thief: The Dark Project is also credited as a pioneer of the genre.
With further releases, many games in the genre have drifted towards action by allowing the option of direct confrontations. The Hitman series, the first installment of which was released in 2000, allowed this play style, but rewarded the player for stealthy and elaborate assassination of antagonists. Hitman: Codename 47 was also the first 3D game to employ the genre's device of disguises. No One Lives Forever, an espionage themed parody also released in 2000, again allowed the player to combine or choose between stealth and overt violence. The survival horror series Silent Hill, which began in 1999, also gives a choice between direct combat or avoiding confrontation, by making use of the fog to dodge enemies or turning off the flashlight to avoid detection, helping to preserve ammo as well as health. In 2000, the first-person action role-playing game Deus Ex also incorporated stealth elements in its gameplay.
The acclaimed Metal Gear series continued with Metal Gear Solid 2: Sons of Liberty (PlayStation 2; 2001) which further evolved the stealth gameplay. It featured an array of new abilities, including "leaping over and hanging off of railings, opening and hiding in storage lockers," and sneaking up behind enemies to "hold them at gunpoint for items and ammunition." The environment also had a greater impact on the stealth gameplay, taking into account factors such as weather, smell, atmosphere and temperature. The game also introduced a collective enemy AI, where, unlike previous games in the genre, the enemy guards in Metal Gear Solid 2 work together in squads, can communicate with one another, and react in a more realistic manner towards the player. The game's enemy AI was considered among the best examples in gaming for many years. The game also expanded its predecessor's cover mechanic, with Snake or Raiden now able to take cover behind walls or objects and pop out to shoot at enemies, while the enemies could also take cover, and pop out to shoot at the player or throw grenades. Metal Gear Solid 2: Sons of Liberty became the genre's best selling game with 7 million in sales, followed by Metal Gear Solid with 6 million in sales.
Later developments: 2002–present
Due to the success of Metal Gear Solid, and to an extent Tenchu and Thief, stealth elements have become increasingly incorporated by a wide range of video games, with numerous action games since then using stealth elements in some way or another. 2002 saw the first instalment of the Tom Clancy licensed Splinter Cell series, an attempt at a more realistic game in the vein of Metal Gear. As with Metal Gear, if the player is discovered in Splinter Cell, the guards will often raise a general alarm. This can cause a difficulty spike or even result in automatic mission failure.
Sly Cooper, a cel-shaded game released in 2002, was a "stealth platformer", while 2003's Siren combined the survival horror genre with the stealth genre. That same year, Hideo Kojima's Boktai was a unique stealth-based action role-playing game that made use of a solar-power sensor to detect light. The following year, Konami's Metal Gear Acid combined the stealth gameplay of the Metal Gear series with turn-based strategy and tactical role-playing game elements as well as card battle elements from Konami's own Yu-Gi-Oh games.
In 2004, Metal Gear Solid 3: Snake Eater (PlayStation 2) introduced camouflage to the genre. Set in a jungle, the game emphasized infiltration in a natural environment, along with survival aspects such as food capture, healing and close-quarters combat. The following year, the updated version Metal Gear Solid 3: Subsistence introduced an online multiplayer element to the genre.
In 2007, Assassin's Creed employed a social element to the stealth game, where the player is able to hide among crowds of civilians by taking care to blend in. The same year, Crytek's open world first-person shooter Crysis incorporated stealth elements within its gameplay, as did the multiplayer first-person shooter Team Fortress 2 the same year and the first-person role-playing game Fallout 3 the following year. In 2008, Metal Gear Solid 4: Guns of the Patriots (PlayStation 3) introduced a battlezone element, where the stealth gameplay is incorporated into a battlefield fought between two armies, both of which can be infiltrated by Solid Snake. In 2009, Assassin's Creed II broadened its predecessor's elements of stealth by allowing the player to blend among any group of civilians, rather than specific ones. Assassin's Creed II also allowed the player to distract guards by tossing coins or by hiring thieves and courtesans, and also featured a notoriety level, which made the player more recognizable until they paid off officials or tore down wanted posters.
Metal Gear Solid: Rising, an early version of the action game Metal Gear Rising: Revengeance, was initially planned to feature stealth gameplay that emphasizes considerable speed and agility through what is described as "hunting stealth." Unlike the "waiting stealth" of previous titles, in which players remain hidden and avoid combat, players in Metal Gear Solid: Rising would have instead quickly stalked their enemies and used acrobatic maneuvers to stay out of sight while closing in. The game was also intended to have a moral element, rewarding the player for avoiding the unnecessary killing of human enemies.
Metal Gear Solid V: Ground Zeroes is considered the next step forward for stealth games. Its "good failure design is one that is less abusive to you, by replacing its hard game-over screens, or reasons to simply quick-load, with mechanics that extend or alter gameplay beyond failure in interesting and engaging ways." It is also the first open-world stealth game where "the whole environment is enemy territory. Nowhere is safe. That's standard operating procedure for Snake. But the sheer scope of Ground Zeroes' open-world approach creates a vast playpen of interconnected systems that exist to nudge you closer to, or further from, failure." 
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