Metal Gear REX

Metal Gear REX is a nuclear-equipped bipedal tank that was jointly developed by DARPA and ArmsTech Inc for the United States Army in the early 2000s that based from designs from the Cold War during the 1960s.

Background
In the early 1960s, Soviet scientist Dr. Aleksandr Leonovitch Granin had created designs for a REX-like bipedal tank. While Granin's colleagues critized his ideas, an American colleague supported it and also wrote a paper on the topic of walking tanks that ended up highly-criticized.

In 1964, Granin had hoped to use GRU Colonel Volgin's deep pockets fund a "Metal Gear" project. However, Volgin rejected Granin's ideas in favor of Dr. Nikolai Stephanovich Sokolov's Shagohod, believing that Granin's ideas weren't worth while. Afterwards, a drunk and bitter Granin sent the designs to his friend in the United States, revealing this to CIA agent Naked Snake. Later, the Philosophers' triple agent Ocelot stole duplicates of these designs and delivered them to his superiors.

Post-Snake Eater
The designs later served as the inspiration for several weapons:
 * In 1970, it served as Sokolov's inspiration of the Intercontinental Ballistic Metal Gear and Metal Gear RAXA for the CIA and the DoD.
 * In 1974, it served as Dr. "Huey" Emmerich's and Dr. Strangelove's inspiration of the Chrysalis AI weapon for the Peace Sentinels and later Metal Gear ZEKE for the Militaires Sans Frontieres.

Metal Gear REX Project
Some time after Solid Snake's encounters with Metal Gear TX-55 in 1995 and Metal Gear D in 1999, an attempt to carry out a Metal Gear project within the United States had been planned, but was officially scrapped. However, the private weapons company ArmsTech (which had been in a dire state financially, with the possibility of a hostile takeover becoming apparent after failing to obtain the contract for a new line of fighter jet) convinced the U.S. Army that building one would be a very profitable venture.

In 2002, DARPA Chief Donald Anderson was heavily bribed by Armstech President Kenneth Baker to back the Metal Gear REX project, and to fund its development covertly, using part of the United States' black budget. The nuclear weapons disposal facility on Shadow Moses Island was constructed to hide the development of REX. REX's rail gun was based on the rail gun for the SDI, and miniaturized for REX by a joint venture between ArmsTech and Livermore National Labs.

One of the main goals of developing REX was to overcome a global trend in military downsizing at the time. A weapon such as REX would cause an immediate rift in the global power structure. REX was capable of launching a nuclear warhead without the need for a rocket propulsion system, making it undetectable by radar. It could give any country in the world a first-strike capability that other nations would find hard to counter. This also exploited a specific loophole that existed in anti-nuke treaties, since weapons fired from a rail gun were not technically ballistic, so limitations on ballistic weaponry did not apply.

During REX's development, the Metal Gear engineers became concerned of what would happen if REX, after it was completed and doing solo ops overseas, had to engage in close range combat. They then decided that they could make REX's hull a weapon in itself. Although the program was completed, and had gotten fantastic results from supercomputer simulation, the military shelved the project before they could even install it (as the military viewed it as not being part of their regulations). However, REX's chief engineer, Dr. Hal Emmerich, secretly uploaded the data into REX anyway.

In 2005, Baker and Anderson attended a rail gun testing exercise at the nuclear weapons disposal facility on Shadow Moses Island. However, REX's prototype was captured by the special forces group FOXHOUND, which had originally been assigned to oversee the final testing of the secret new weapon. The threat of a nuclear attack was used in an attempt to extort Big Boss's remains from the U.S. Government and later $1 billion.

Hal "Otacon" Emmerich was opposed to nuclear weaponry, and it was unlikely he would have assisted in the program if he had known REX's true purpose. He was informed that REX was intended for intercepting nuclear weapons and that REX's armament was handled by a separate department to keep him in the dark. Their development and integration into the main chassis were out of his control, and as far as he knew, these armaments were intended to defend the REX unit itself, and to provide Theater Missile Defense.

It was only during the Shadow Moses Incident that Otacon discovered REX's true purpose as a nuclear launch platform, and its revolutionary delivery system – a railgun. As the projectile it fired was not actually a missile, it wasn't covered by current disarmament treaties. Even worse, the combination of the size, speed and nature of the projectile could allow the payload to bypass current missile detection systems, which had always been dependent on the characteristics of missiles – size, speed, and propellant exhaust – to track them.

REX was the ultimate Metal Gear, as it was not only capable of delivering a nuclear weapon both to and from any point on the globe, it could do so "undetectably" and "untraceably." All previous Metal Gears were merely mobile ground-based launch systems for nuclear missiles, little more than the land-based equivalent of ballistic missile submarines. REX utilized a rail gun, which fired much smaller projectiles without chemical propellants – factors which made them virtually invisible to radar. It thus fatally undermined the 'no first strike' principle of Mutually Assured Destruction – whoever controlled it could launch a nuclear attack at any target at any time, with no warning before impact.

It became clear that REX was in fact to be used to make the nuclear strike; Otacon took it as his duty as REX's creator to destroy it. Liquid Snake and Revolver Ocelot later intended to join forces with former-Spetsnaz colonel Sergei Gurlukovich, with REX on their side.

After Solid Snake unwittingly activated REX via the PAL system, Liquid piloted the weapon in an attempt to kill him. Snake, using Otacon's advice, was forced to destroy REX’s radome using Stinger missiles, and after several successful hits, the machine was temporarily immobilised. However, the missiles caused less damage than Snake expected, and REX became fully operational once more, attempting to crush Snake beneath one of its feet. Before this could happen, Gray Fox (as the Cyborg Ninja) intervened, using his cybernetic-enhanced strength to hold up REX's foot and thwart its attack. Gray Fox then damaged REX's radome further, with several blasts from his exoskeleton's gun and his sword, allowing Snake and Fox a temporary respite. Providing Snake with additional missiles, Fox attempted to halt REX's advance, but his left arm was dismembered from his body by REX's laser, and he was eventually pinned against a wall by its "beak" cockpit. In an act of sacrifice, Fox got off a few more shots from his gun, succeeding in destroying the radome completely, and forcing Liquid to open the cockpit, though he was promptly killed beneath REX's trampling feet.

Now having the chance to finish off REX, Snake managed to launch a Stinger at its cockpit. As Liquid proceeded to step on Snake with REX once more, the machine suddenly began to lose its balance, the cockpit having become inoperable from the damage sustained, and the resulting explosion knocking Snake unconscious. Still standing strong, Liquid dragged Snake to the top of REX's head, where the two engaged in a bare handed fight. At the end of the deadly battle between the two, Snake's finishing blow knocks Liquid off the top of the Metal Gear, though he would survive the fall to the ground below.

The Shadow Moses Incident placed the plans for REX's mass production on indefinite hold, and the entire development was scrapped.

Post-Shadow Moses
Following the 2005 incident, Revolver Ocelot ended up supplying the REX data to Solidus Snake after the events of the incident and later leaked the Metal Gear exercise data he had acquired there to the black market, unleashing a swarm of Metal Gear derivatives throughout the world. In response, Solid Snake and Otacon formed the anti-Metal Gear NGO Philanthropy, and sabotaged as many Metal Gear development operations as they could; the U.S. Marines' response was to develop Metal Gear RAY, a new Metal Gear hunter-killer to eliminate REX derivatives.

In the meantime, the original prototype lay wasted and abandoned in the underground maintenance base where it had been destroyed.

In 2014, Liquid Ocelot returned to Shadow Moses Island and salvaged the railgun from the remains of the original Metal Gear REX, with which to launch a nuclear strike on the Patriots' master AI. Since it had been developed before the introduction of the SOP System and had laid untouched since 2005, it was the only WMD that could be used to make such a strike. Old Snake (Solid Snake) returned to Shadow Moses himself in an attempt to stop Liquid, but was too late. Instead, he encountered Vamp and fought him, until Raiden took over for Snake. Raiden and Vamp fought on top of REX, resulting in Vamp's death. Otacon, via Metal Gear Mk. III, managed to re-power REX, allowing Snake to pilot it out of the base, while fighting through hordes of Suicide Gekko. Upon arriving at the surface, Snake was confronted by Metal Gear RAY, which was being piloted by none other than Liquid Ocelot. Despite the fact that RAY had been specifically designed to destroy REX, and the latter was handicapped due to its inoperable radome, Snake (with Otacon's assistance) managed to destroy RAY with REX shutting down soon after.

Information
Metal Gear REX is operated by a single pilot, who has no direct view of the cockpit's exterior; information is instead gathered by a sensor package in a radome on the left shoulder of REX, and passed on.

Radome
The radome is a satellite-shaped object on the left side of Metal Gear REX that provides information about the environment outside of the cockpit while keeping the pilot safe from harm, and increasing the accuracy of all weapons as well.

Destroying the radome is crucial to rendering the virtual reality interface useless and forcing the pilot to manually control REX. The pilot is also forced to expose himself to enemy fire, by opening the cockpit in order to see outside.

Armament
REX differed from earlier Metal Gear models in that its legs were heavily armored and reinforced; not vulnerable like its predecessors. Along with near-impenetrable compound armor (of which only HEAT weapons could deal sufficient damage) and a TMD missile module on its back, REX also had a pair of 30mm Vulcan cannons, knee and back-mounted anti-tank missiles, and a high power free-electron laser, to protect itself from conventional forces. Its feet also possessed retractable metal stake-like protrusions, which were used to find purchase on difficult terrain, and could be employed in "stomp" attacks on an enemy.

The anti-tank missiles on both of REX's knees and back were a laser semi-active homing type that didn't use wires. The launchers used a laser illuminator to bounce a laser beam off a target that the missile would then home in on. The free-electron laser mounted on REX's belly was capable of generating close to 100 megawatts of energy, ten times greater than any other laser at that time.

REX's most fearsome weapon, however, was the magnetic railgun capable of delivering an untraceable nuclear warhead anywhere in the world, without the propellant trail or launch flare that gives away the launch position of a traditional ballistic missile. By perfecting the process of shell acceleration, the railgun is able to fire a projectile with a muzzle velocity of over 100 kilometers per second. It was originally going to be used, as part of SDI, to shoot down enemy ICBMs outside the atmosphere.

During Liquid Ocelot's Insurrection, Otacon revealed to Old Snake that he had installed a 'Street Fighter' program into REX that gave it not only an agility boost, but enabled the Metal Gear to execute kicking and other melee moves, which would be lethal to many military vehicles and other Metal Gears such as Metal Gear RAY. This program was one of REX's most lethal weapons compared to its other conventional warfare weapons, as military vehicles and Metal Gears were designed with countermeasures against conventional armaments, but not the raw brute force of these attacks.

Trivia

 * REX is named after the Tyrannosaurus rex, due to its theropod-like design; other similarities include its ability to roar, and the open cockpit's resemblance to a gaping mouth. "REX" was also the Allied codename used for the Japanese Kawanishi N1K floatplane during World War II.
 * After the cancellation of the Arsenal Ship Project in 1996, following the death of the 25th Chief of Naval Operations, the Pentagon's Black Budget was freed up, allowing the REX Project to proceed undelayed. Though the CNO's death was officially ruled as suicide, rumors to the contrary circulated at the time.
 * Metal Gear REX was foreseen in Elisa and Ursula's psychic premonition in 1970.
 * Though designed for the purposes of eliminating Metal Gear REX derivatives, Metal Gear RAY, manned by Liquid Ocelot, was defeated by the original REX model in 2014, with Old Snake as its pilot. In a similar manner, Solid Snake (the "inferior" clone of Big Boss) was able to defeat Liquid Snake (the "superior" clone of Big Boss) in physical combat in 2005.
 * In latin, "Rex" is a word meaning "King".

Metal Gear Solid
The first Metal Gear to appear in 3D, REX's appearance (with numerous flat surfaces and little exposed wiring) was tailored with the graphical limitations of the PlayStation console in mind.

The Metal Gear Solid Official Mission Handbook gave a list of specifications regarding Metal Gear REX. However, details regarding the machine guns and air ordinance are incorrect, putting the canonicity of this information in question:

METAL GEAR REX - STANDARD MECH DEFENSE MACHINE WALKING BATTLE TANK (WBT) - REX0023b ''' Crew: 1 (nose cockpit) [Armament] Machine-guns: 2xg12.7mm in the nose (covering 60° arc to the front) Air ordinance: 3xPhalanga-F (AT-3 "Rain from Heaven") Radio-guided anti-troop missiles Rail Gun: 18.5m Rail Gun (Special Ops Optimum Bombardment 422 "Widowmaker"), launch tube: Standard (conventional, nuclear) Laser: ArmsTech International V17 Vulcan Cannon, Searing LaserStorm High Energy Cutter "Slice n' Dice" (covering 90° arc) Ammunition: 10,000x12.7mm, 72xPhalanga-F Reds, Laser Pro Pack, 1xCruise AGM-129 ACM Length (gun forward): 18.9m Length (hull): 7.455m Width: 5.760m Height (gun forward): 12m Height (gun up): 13m Weight (combat): 505,450kg Power-to-weight Ratio: 450hp/ton Engine: ArmsTech AGM 4000 "Behemoth" Maximum Road Speed: 140.777km/h Maximum Range: 1,505km Fuel Capacity: 5,550lit Armor (type): Laminate/Steel NBS System: Yes Night Vision Equipment: Yes''
 * ' ARMSTECH LAND SYSTEMS DEPARTMENT

Metal Gear Solid 4: Guns of the Patriots
In Metal Gear Solid 4, the anti-tank missiles are described as being radio-guided in REX's "AT missile" weapon description, despite Otacon mentioning that they were laser-guided in Metal Gear Solid. REX is the first Metal Gear to be playable in the series (not counting the Metal Gear Mk. II and Mk. III). While piloting REX, pressing the Triangle button will cause REX to "roar." Though it was REX's left foot that killed Gray Fox, taking a picture of its right foot will cause the ghost of Gray Fox to appear.

Super Smash Bros. Brawl
Metal Gear REX appears alongside Metal Gear RAY and Metal Gear Gekko on the Shadow Moses Island stage in Super Smash Bros. Brawl.

It also appears as a sticker and trophy with the following description:

"A war machine of ruinous power. Metal Gear REX was developed at the weapons company ArmsTech under the eye of Hal 'Otacon' Emmerich. It had the ability to launch nuclear warheads from a mounted rail gun. During testing, REX was captured by FOXHOUND, a rogue special-forces unit headed by Liquid Snake, but Solid Snake managed to destroy the machine before calamity ensued."

Metal Gear Solid: Peace Walker
In Metal Gear Solid: Peace Walker, a secret boss can be encountered on Monster Island called "Gear REX," which has several striking similarities to Metal Gear REX, such as bone ridges that make its face look like the Metal Gear, and a limb over its right shoulder representing the railgun, which shoots a highly acidic mucous instead. Its roar also sounds similar to that made by its namesake.

Although Otacon talks about the railgun having been successfully minitiarized for REX, in the original Metal Gear Solid, a similar-sized weapon appears on the Chrysalis AI weapon and Metal Gear ZEKE despite this.