M6A1 Raider Main Battle Tank

the M6A1 Raider Main Battle Tank was the primary heavy armoured vehicle used by the United Nations Space Command following the Human-Covenant War. Replacing the venerable M808B Scorpion MBT in the main battle tank role, the Raider was up-armoured and up-gunned from its predecessor, while being faster, lighter and more capable against soft targets. Incrementally replacing the Scorpion from 2558 over a period of seven years, the Raider's flexibility made it widely used by the UNSC Marine Corps, who benefited from its superior speed and agility without compromise of armament or protection. Seeing widespread usage against Covenant forces, the Raider surpassed even the Scorpion's effectiveness in battle against enemy infantry and armour.
==History==
===Development History===
The Raider was tasked with following in the prestigious footsteps of the preceding M808B Scorpion Main Battle Tank and its many variants, which had amassed a well-deserved reputation in the Marine Corps as a potent vehicle. The Scorpion was well-armed, more than properly armoured, lightweight enough to be airlifted and fast enough to keep pace with mobile armed convoys made up of other ubiquitous Marine vehicles, such as the M12 Warthog LRV. It was also armed with a 90mm High Velocity Cannon, which was capable of engaging both infantry and light armour effectively and heavier armour too, although to a lesser extent. Where it lacked was its acceleration, and defensive armaments, both of which were areas the Raider set out to improve on. The Raider had a maximum speed over rough terrain of 75kph, and over smooth surfaces it could reach 90kph, significantly improving its mobile fighting capability over its predecessors. Improving significantly over the Scorpion would be no easy task, but with the help of several design innovations, including an improved autoloader to increase rate of fire, a plasma fusion drive to increase power, and more secondary armaments for self-defence, in addition to advanced composites and metamaterials, the Raider lived up to and surpassed the reputation of the Scorpion. Popular and effective throughout Marine service, the Raider incrementally replaced the M808B from 2558 onwards; it completely superseded it in the Main Battle Tank role from 2564, although the M808 continued to see use as an armoured recovery vehicle and armoured bridge layer until the late 2580s.
===Operational History===
The Raider fired its first shot in anger in 2559 at the First Battle of Petrograd, where it successfully outperformed enemy Wraiths, and also took a heavy toll on light armour and infantry. Raiders made up a large portion of UNSC armoured forces that successfully held the colony's capital through almost three days of Covenant attacks, until relieved by Marine reinforcements. Following this, they led the armoured charge in the UNSC counterattack to force Covenant troops off the planet, while the Navy eliminated their warships. Initial reports showed the Raider held up well in combat, though there were issues with its side armour jamming the treads after prolonged plasma damage; the issue was rectified with the addition of another layer of plasma-ablative coating. In 2567 it was negated by the addition of anti-plasma countermeasures, which disrupted the magnetic containment fields of plasma bolts.
Later, in 2568, large numbers of Raiders participated in a full-scale UNSC invasion of the Covenant-held world of Perseus-9. Raiders made up the heaviest of the UNSC's deployed ground forces, engaging with Covenant heavy armour such as the Covenant's Type-25/Improved Assault Gun Carriage. Three M6A1s of the initial invasion force ambushed a Scarab and intercepted it before it reached a friendly landing zone, destroying it with a total 27 rounds to its vulnerable rear. The battle was an eventual victory for the UNSC, demonstrating their ability to attempt and succeed at large scale offensives. During the battle, Raiders accounted for a total 205 confirmed enemy Wraith kills, with a further 718 light vehicle kills and 238 assists, for a loss of twelve Raiders.
During the Covenant's Invasion of Whitefall in 2569, the the small colony came under surprise attack from Covenant forces, with little UNSC presence on the planet. During the invasion of the Covenant Army through the Odin Mountains, a natural barrier protecting the capital of Obelisk, two damaged Raider tanks engaged approximately 150 Type 25 and Type 25/I tanks and three Scarabs. In the course of the following 30 hour battle, the two tanks knocked out over 60 enemy vehicles. The losses of this armoured division forced the Covenant army to halt their advance, as they lacked sufficient numbers to protect their planned infantry assault afterwards. Reinforcements arrived hours later in the form of the UNSC 18th Taskforce, which evicted the Covenant presence from the system.
==Usage==
The Raider filled the role of a Main Battle Tank or MBT, meaning it was designed to be a well-rounded tank design capable of at least limited operation in any armour role found on the battlefield. Its usage was widespread and varied, being able to engage most threats and dispatch them in the vast majority of standard and extreme environments. It was a capable anti-armour unit, effective against infantry, low-flying aerial targets and opposing tanks. It was well-armoured enough to render it almost invulnerable to both conventional and non-conventional weaponry, and was mobile enough to keep pace with smaller, less well-armoured tanks, enabling it better function in theatres such as urban warfare. They often made up the staple of UNSC armour forces as their all-round ability meant they had better chance of dealing with unexpected events, far more so than dedicated tank destroyers, infantry fighting vehicles or light tanks.
The M6A1's speed, light weight and above all, flexibility made it extremely useful in its service with the UNSC Marine Corps, who focused on rapid, firepower and strategy-oriented assaults relying on overwhelming speed and strength to take enemy positions. In this way it was inkeeping with Marine standards and tactics and was easily deployed from orbit as part of Marine planetary assaults.
The M6A1 Raider was used almost exclusively in the UNSC Marine Corps, while the Tarantula Main Battle Tank was used by the UNSC Army. The Tarantula was better armed, featuring a 150mm main gun, though was not capable of flexible operations the Marines required as it was almost nineteen times heavier.
==Design Features==
The exterior of the Raider MBT appeared as a cross between the exotic Scorpion and the upgraded Grizzly variant, featuring the latter's heavier turret and expanded internal area. The Scorpion did not have an internal compartment as such and, while this is not reflected in the Raider, it does take many design elements that made the Scorpion family so successful from both vehicles. Featuring a quad articulated tread layout, the Raider was better capable of navigating difficult terrain at high speed, featuring average acceleration of 12m/s2 but an impressive top speed of 90kph. The layout also reduced the chances of an M-kill or mobility kill, disabling the tank's drive system resulting from enemy fire. The chassis, based on that of the Scorpion's, was nonetheless heavily updated, being larger and more resistant to enemy fire. The turret, like the chassis, was similar to the Scorpion's, though was noticeably more angular to better withstand plasma impacts and deflect projectile weapons fire. The front of the turret featured the elevating main 120mm gun on the left and the separately mounted dual 20mm cannons on the right. The tank was constructed with the aid of both Covenant and Forerunner composites and metamaterials, meaning that, although significantly larger than the Scorpion, it weighed seven tons less at 59 metric tons. This meant that it exceeded the Scorpion's airlift capability and could be deployed easily by Pelican Dropships.
The interior of the M6A1 was arranged in a conical layout, with the Driver's compartment to the center and left of the vehicle. The main gunner was located in his specialised seat in the center right. Both the Driver and Gunner sat in the center of the turret ring, this position reduced pitch input to the occupants allowing them to drive at higher speeds and ability to perform to their full capability during high off-road speeds. The plasma fusion engine was to the Raider's rear, separated by an armoured fireproof bulkhead. To the rear of the driver/gunner area was the engine compartment, resting along the midline and centre of the tank and providing the best balance for the vehicles suspension.
Inside the two person turret the secondary gunner and tank commander sat on either side of the autoloader, the Commander separated by an armoured bulkhead from the main gun. The secondary gunner's compartment on the left side of the turret was open to the autoloader to allow him to provide repairs or manually load the gun as needed. The bulkheads in the design allowed for a higher structural spatiality, and better shock resistance to the Raider's frame due to impact or other stresses. It also provided continued survivability even after loss of the autoloader in the more vulnerable turret, compared to the Driver or Gunners compartment. The secondary gunner would, in the event of the autoloader being disabled, be capable of hand loading the shells, decreasing the tank's capabilities but maintaining the lethality of the main gun at full capacity, even with reduced operational rate of fire.
To the front of the turret was the secondary ammunition storage compartment, self sealing fuel tanks and auxiliary hydrogen hybrid engine which provided supplemental power to the system. This allowed for immobile 'silent' operation in a defensive stealth role with little to no thermal signature, and the ability to passively range and strike an enemy target. As a result the Raider could make long range kills without the need to expose itself or draw unwarranted attention. At the very rear of the tank was the combined Exhaust and Radiator compartment which not only provided a significant reduction in the vehicles thermal signature but the extra bulkhead and equipment allowed for better protection of the powerpack, and for a cooler exhaust which increased the vehicles survivability. As such, a strike to the lightly armoured rear of the vehicle was not generally a lethal hit; though it could significantly lower the tank's capabilities, the vehicle would most likely still be capable of maneuvering, returning fire and such long enough to retreat to safety.
===Fighting Compartment===
The fighting compartment of the M6A1 was a stark contrast to most tanks of its era, and affected all subsequent modern tank designs. MPHDs or Multi Purpose Holographic Displays were mounted in each station, allowing for high contrast touch operated full colour control stations that allowed for smoother and more efficient use of each stations' available space. This also enabled the ability to 'hand off' certain functions to another position should a station become damaged or a major injury sustained by a crew member. This ability allowed for increased vehicle lethality even when damaged. Short of a lethal strike to the drivers compartment all offensive and defensive functions can be handed off as needed to allow even one person to control the functions of the vehicle, though admittedly at a decreased level of efficiency. 
The Driver's compartment at the center left of the vehicle contained a partially reclined shock absorbant seat that made a smoother ride for the driver, as he/she was the closest to the suspension and likely to take the most abuse during high speed cross-country travel. To either side of him were MPHDs that could provide full details of the vehicle's current capabilities including speed, power, damage sustained, percentage of slack in the tracks, etc, thanks to a localised grid of sensors. As well as displaying images from the armoured rear view camera and passive observation via the commanders sight, all sensory data was displayed here such as possible targets, terrain and sensor readings. The driver also had the usual three periscopes which provided a 180 degree panoramic view, with a VISTA Sight covering the forward 60 degree arc to provide all weather day or night driving capabilities with no need for external illumination. All stations displayed sensory data fed directly from the sophisticated sensory package. 
The main gunner's station was very tailored to its role. It had two MPHDs for ammunition selection, autoloader programs and such, but the main work was done with their eyes in the sights. Just like the driver's compartment, the seat was partially reclined, with the MPHDs and main sight on a sliding system that allowed them to be brought forward once strapped into the seat. This meant less strain on the gunner's back and shoulders and an overall more comfortable shooting position. During a dismount, or entering the vehicle the station was slid back and locked into place so as to not get in the way of the operator.
The Commander's station was situated in the turret above and behind the main gunner's station, with the gun bulkhead and autoloader separating him from the secondary gunner's compartment. The Commander's station contained three MPHDs which helped provide navigational and GPS data that could then be transferred in real time to the driver or an entire company, allowing for highly accurate deployment of combined arms forces. Attached to the Commander's helmet along with a microphone (for the internal, short range, and long range radio systems), was a Commanders Personal display HUD which could be pulled down to cover the commander's right eye. This system directly controlled the compound individual target sight located on top of the M41 LAAG turret (known as the OWS or Overhead Weapon System), and rotated in conjunction with the commanders head. This allowed the commander to lay down defensive fire without compromising his situational awareness, or exposing himself to battlefield hazards. This system, though seemingly complex, was almost identical to the system employed by virtually all UNSC aircraft. This allowed the commander increased situational awareness without decreasing his ability to keep a close eye on the other functions under his control. The target selection, lock and unlock of the head following functions, and reticule control were controlled by the commander's right hand via a multi-function joystick, and controlled the prompts on his personal display, while the left hand was free to use the other MPHDs as needed for navigation, fire control, etc.
The secondary gunner or specialist was located across from the Commander and above the Driver. While the idea of a fourth, barely needed crewmember was in theory impractical, in reality it was extremely beneficial to the tank and its crew, both in and out of battlefield situations. Trained as a dedicated vehicle engineer, he was responsible for keeping the tank fully operational and combat ready when operating far from a friendly command post. When in combat the specialist acted as both the Defensive system operator, as he oversaw the mode and effect of both automated M40 Self Defense Munitions Launchers and M56 Point Defense Weapon System. In addition, he operated as a valuable close range defensive fire gunner of the single AIE-486 .50cal HMG, which could be controlled either manually through a hatch or remotely via the OWS. The Specialist also had control of an similar OWS to the Commander's, increasing the tanks versatility and defensive firepower significantly. He also acted as a loader in the case of an autoloader or power failure as may well be required, or in any sort of support role that may be needed.
==Armament==
===Main Armament===
The M6A1's primary armament was its M1105 120mm Cannon. An increased calibre over the M808B's 90mm Cannon, the M1105 was more effective against Covenant armour, its round often dispatching Wraiths and their variants in a single shot, and proving capable of serious harassment of Scarabs. Rate of fire was vastly improved as well; the gun featured an advanced high speed autoloader which stored ten rounds ready for firing in a sort of internal magazine. After these rounds were expended the weapon needed to return to a 'static' inoperable position to reload the magazine, which took just over nine seconds to reload all ten rounds. The main gun could empty the magazine in just 3.8 seconds if required, giving a total rate of fire of 159.9 rounds per minute. The single rotor was mounted directly to the gun carriage and elevated with the gun. The rotor contained five slots each holding two rounds each, allowing for any number of the ten rounds to be fired selectively. This system offered full inventory control, by means of integrated RFID tags, optional round replacement, unloading, and misfire ejection. Full emptying of the magazine in a single exchange of fire was not often done as it left the then-reloading tank vulnerable to return fire; it was often undertaken against heavy targets or multiple spread out ones; the autoloader meaning the gunner would not have to wait for rounds to reload before he could fire again.
The Raider's additional 70 rounds were stored low in the rear of the hull in a reserve magazine designed to automatically transfer rounds from the reserve magazine to the ready magazine. This arrangement made the entire complement of 70 rounds available without the crew leaving its compartment. Complete reloading of the Primary Ammunition rotor took just under a second per round and was completely automated. The autoloader compartment in the bustle, as well as the primary storage of rounds, was protected by a series of blow-out panels that prevented an ammunition explosion from destroying the fighting compartment and subsequent death of the crew, should a critical hit compromise the bustle of the turret or the primary reserve.
Partly to control the high recoil when firing rounds in short succession, the Raider featured a GRAD or Gas Recoil Attenuation Device installed to improve main weapon lethality. It used an unconventional fume extractor to pressurise a pneumatic recoil attenuation device, in a fashion similar to a gas delayed blowback mechanism in firearm, however on a much larger scale and with a different purpose. It lowered the total transferred recoil of the gun before it was transferred to the body to be absorbed by the relative mass of the tank, allowing the high velocity cannon to put less strain on the overall frame of the vehicle. The gun mount, which mounted both the main gun and the coaxial autocannons, was stabilised on two axes and could provide a perfectly solid firing platform while moving at up to 70kph on open terrain, and a suitably level platform up to the Raider's top speed of 90kph. The long barreled freebore gun could propel a round downrange at a lethal 8,238 m/s, to targets up to 29km away even while on the move. At these velocities the 120mm High Pressure Cannon could achieve massive penetration at optimal ranges and do it repeatedly as a result of the high speed autoloader. Installed RFID tags in the projectile allowed for the tank commander to designate both a target and ammunition type which would either automatically load the required round in sequence, or prompt the specialist to hand load a round as may be required. The M1105 was a weapon of great effect in the hands of a trained gunner. The gun tube's effective combat life was rated at upwards of 1500 rounds.
Rather than a smoothbore or rifled barrel, the M1105 used a unique 'freebore' type which improved its performance. The Freebore Pneumatic Effect Cannon or FPEC was quite different to its predecessors which used the less efficient barrels. The questionably efficient ‘rail and groove’ method would allow for the entire length of the groove to be open to both the front of the round and the propellant gases. This would lead to any turbulence possibly allowing propellant gas to escape and to increase the area that the gas expands into, decreasing the cannons overall efficiency. Replacing this method was a much simpler technique of 120 cells, 2 centimetres in diameter and 4 millimetres deep, arranged in twelve rows of ten cells. When a round was fired, the vacuum generated by the mass of air being distorted by the movement of the round was sucked around the aerodynamic shape of the round. The path of least resistance for the first 'block' of air in front of the projectile was to be pushed to the side, and the remaining turbulence forced the air into the 120 cells. The air remained pressurized in the cells by both physical occupation of space, and air turbulence. This method also prevented propellant gas from behind the round from slipping out as the inner bore was fully occupied by either the sabot or projectile. The barrel was subjected to more stresses than standard smoothbore or rifled ones but was much more efficient and allowed for higher velocity, accuracy and range than conventional barrel types. The round would be subjected to a much more constant acceleration down the barrel, as well as markedly reduced friction. The round benefited from a much flatter ballistic trajectory, meaning longer ranges were possible with the same degree of accuracy.
===Secondary Armament===
Supplementing the main gun were a pair of coaxially-mounted M3911 30mm autocannon. While mounted on the same stabilising platform as the main gun, they had a separate elevation than the main gun allowing it to elevate up to 60 degrees to engage low and medium level aircraft of all types at ranges up to 3km with maximum effectiveness. The dual feed allowed the gunner to choose between Armour Piercing Incendiary (API) and High Explosive Programmable Air Bursting (HEPAB) rounds at will, to provide the best possible lethality against the target. The HEPAB round contained an minute electronic timer, an ejection charge and 130 cylinder-shaped tungsten alloy bars or sub-projectiles. The electronic timer was programmed by inductive coupling through a device installed in the muzzle of the cannons. The timer initiated the ejection charge which released and dispersed the tungsten projectiles before impact with the target. These powerful coaxial guns were chosen to lessen the strain on the main gun, and provide more effective air protection than an external 12.7mm or 15mm round could provide, freeing up existing secondary weapons for ground defense, mainly lightly armoured or unarmoured vehicles and infantry. The weapons were fed by multiple ammunition feeds, allowing more than one type of round to be used and giving greater dimension to the weapon's use. Due to the use of two rather than one coaxial guns, the rate of fire of each weapon could be decreased while not affecting overall performance.
Both the L120 and M3911 Cannons used the Electrothermal Acceleration method of projectile propellant. The Electrothermal Acceleration system used a plasma discharge rather than a chemical reaction to force the shell down the barrel. A high current, high voltage energy source was used along with a large Capacitor bank. Both were attached in series to the electrode system in the cannon's barrel. The capacitor was loaded with as high a voltage as possible, and the capacitor was then discharged. The gas in the gap between the electrodes would ionise, turning the non-flammable propellant into superheated conductive plasma. At this point, associated volumetric expansion would propel the projectile from the barrel at very high velocity. 
The advantages of this method of propellant were clear. It increased the round's velocity by up to 280% over conventional techniques, aiding in accuracy and penetration characteristics. It used electricity as energy source, eliminating the need for explosive and vulnerable propellants. The power of the round could also be determined, unlike traditional methods. The more energy was supplied the faster the gases expanded, and the faster the projectile was accelerated. This made it possible to select any velocity desired and also allowed the projectile to reach speeds at which it would outrun the burn rate of a conventional propellant.
===Defensive Armaments===
With the coaxial guns opening up the way for better armament in self defense, the focus of the external weapons shifted from defence against aircraft to protection from infantry. The Raider mounted a weapon mount on the topside of the main turret which could accommodate self defense weapons, and another one on the section of the chassis forward of the main turret. While the mounts could accept a wide range of weapons, the most common were a M41 Heavy Machine Gun and an M247 Heavy Machine Gun, although the latter was sometimes replaced with an MG460 Grenade Machine Gun. Instead of the traditional slip ring system, the tank mounted powered upper hatches that rotated with the gun mounts. This allowed the two-section hatch and the gun shield to provide a combined 300 degrees of armoured protection against small arms for the gunner. Digital vision blocks allowed 360 degree thermal vision, and the weapon could be operated with the hatch closed as an internally operated 'Overhead Weapons System'. The mounted weapons were fitted to a quick dismount pedestal designed as a crew defence weapon should they be forced to bail out and take the weapons with them. This system allowed for a dismounting crew to retain some level of defence as well as providing excellent close in support against enemy personnel while mounted.
==Armour==
===Outer Layer===
The outer layers of the Raider's armour were focused more on withstanding plasma attacks, with lower layers offering excellent all-round protection. The outer layer of the armour was an energy-ablative superconductive layer composed of variable property energy-reactive regenerative nanomaterials. This nanomaterial absorbed most of the energy from plasma assaults and used it to increase its own strength, its properties changing according to the amount of energy it recieved. This technology was an evolved form of the plasma-refractive coating used on MJOLNIR Powered Assault Armour, though benefiting from advanced metameterials to turn incoming energy attacks into a defensive ability. As a result the Raider was able to survive a direct hit from a Type 52 Wraith's plasma mortar, and increased resistance against the T52/Improved Wraith's Particle Cannon.
===Modular Armour===
Underneath this somewhat unconventional armour was more traditional alloy/composite armour, which provided excellent protection against ballistic and plasma weaponry. This protection used both modular and fixed armour to provide light weight of transport, while still offering full protection from battlefield threats. Though designed as primarily to counter KE threats, it had excellent CE protection qualities that were further augmented by the implementation of fifth generation Captive ERA. It was also considerably more resistant to plasma attacks than previous composite armours.
The outer layer of the Raider was coated in a matte rubberised polymer spray coating to decrease its UV reflections and to partially distort LADAR and LASER rangefinders. Though the technical merit of this application was questionable it did help prevent corrosion and was shown to somewhat decrease the power of direct laser sources for the purposes of target illumination.
The outer layer of the composite modular armour assisted in holding the outer armour together, and allowed some slight flexibility yet superior density to engage various threats. Resin impregnated Aramid fabric was wrapped around the composite armor to allow the best small arms protection and structural strength. Below the outer layer was the primary KE and plasma defence, a single piece poured Ceramic DCP plate.
The Ceramic Plate was sandwiched between two plates of CVT (Chromium Vanadium Tungsten) and Austenic Steel alloy. The whole assembly then underwent a hybrid DCP/Triaxial-prestressing method in which the preformed, porous ceramic material was soaked in a bath of molten metal, resulting in super-dense material. As the metal cooled the composite of three plates (one of ceramic, and two of alloy) compressed, increasesing both the density and compressibility of the composite dramatically. This process worked at relatively low temperatures and therefore was more economical than previous production methods. The resulting compound could be molded into complex shapes and offered improved protection at significantly lower weight. This by itself was rather effective but was supplemented by several other materials.
Below the outer plate were several overlapping ceramic 'chevrons'. These chevrons forced any round that was able to penetrate the outer plate to then penetrate the chevrons at a much higher oblique angle than the outer plate. This increased the armour's effectiveness not only by changing the penetrator's vector, but by increasing the thickness plasma had to penetrate. These chevrons were suspended in an plasma-resistant elasticised rubber-like polymer that reduced the shock to the overall plate and transferred much of the impact energy outwards, reducing the stresses on the impact plates. it was also capable of reflecting or absorbing much of the damage caused by directed energy weapons. This material also helped break up penetrating HEAT jets and KE penetrators by causing the chevrons to move around under the force of impact and degrading its overall performance.
Backing the composite matrix was a second composite Alloy/Ceramic plate forcing the plasma or penetrator to again punch its way through at a different vector, forcing the round to fold or break up before it can defeat the final plate. The whole composite was then sealed in a wrap of plasma resistant treated aramid fibres to absorb any remaining spall or plasma splash and attached to the base armour of the Raider's hull in sections for easy replacement.
===Base Armour===
The 'Monolithic Armor Plate' (MAP) for the Raider was produced using a process in which sets of inexpensive, thermodynamically compatible ceramic powders (Boron Carbide (B4C) and Titanium-Carbide (TiC)) were blended with thermoplastic polymer binders and then co-extruded to form a fibre. This fibre composite was first braided then woven into the shape of the desired component. The fabricated component was then stacked and pyrolysed to remove the polymer binder and hot-pressed to obtain the base preformed ceramic material for final processing.
The preformed ceramic matrix was still rather porous, and though extremely hard and ductile, was still rather fragile compared to a composite plate. The DCP process avoided extensive shrinkage in the processing of dense ceramic parts, worked at lower temperatures than conventional methods, did not require the use of high pressures and eliminated the need for post-process ceramic machining. The preform was then soaked in a liquid metal alloy bath. The preform absorbed the liquid metal like a sponge; the liquid metal then reacted with the ceramic powder to form a new ceramic compound that filled in pore spaces. The result was a part with a larger internal solid volume, but the exact same external shape and dimensions as the original preform. The DCP method required reaction temperatures of only 1,300C, compared to the 2,000C required for traditional methods, to form very high melting point, covalently-bonded ceramics. Because the final part maintained the shape of the original porous ceramic, post-process reshaping was eliminated. This translated to cost savings for manufacturers, allowing for more armour to be produced.
The finished Composite was extremely dense, lightweight and ductile enough to resist severe impact stress, while providing excellent anti thermal, kinetic and plasma properties and being easy to manufacture and replace when installed in a modular system.
The crew compartment was protected against anti-personnel mines by means of a reinforced composite floor plate, and beveled angled edges that deflected the blast from large anti-tank mines outwards. Nuclear, biological and chemical (NBC) warfare protection was integrated in the crew compartment air conditioning system via collective overpressure and air filter systems. Backup was provided by the crew's individual battle armour, which was equipped with limited NBC resistance. The infrared signature was minimised through special exhaust ducting and 'thermal black' resin coating on the internal compartments. The power pack and crew compartments were both fitted with a halon fire extinguishing and warning system, which was automatically triggered by detection systems, though could be engaged manually by crewmembers via MPHDs or through HUD neural links.
==Countermeasures==
In terms of countermeasures, the M6A1 made use of the most advanced and powerful systems to improve its survivability. The main system was an M56 Point Defense Weapon System. It was used to intercept incoming ordnance at very high speeds, increasing the survivability of the vehicle. It offered virtually impervious resistance to shells both direct and indirect fire, missiles and other guided warheads, and grenades, mortars and other munitions. It was ineffective against energy weapons. The M56 featured a unique 360 degree simultaneous fire, utilising a high powered free electron LASER to intercept incoming ordnance, and operated on the same basic principle as the Weapon/Anti-Vehicle Model 6 Grindell/Galilean Nonlinear Rifle, or 'SPARTAN Laser'. It was linked to the primary sensor and targeting arrays of the vehicle it was mounted to, though possessed its own shorter ranged sensor systems in case the tank was disabled. Upon detecting an incoming projectile, the device would fire a high-powered, tightly concentrated beam using a very narrow beam confinement, to focus the energy in the smallest possible area. It could detect, fire and destroy any incoming ordnance within a 9km radius virtually instantaneously, defeating even the fastest missiles and shells before they came near the vehicle. The weapon was highly powered enough to allow destruction of even armoured torpedoes and missiles, though was ineffective against armoured vehicles. It could be used against infantry but this meant it was unable to engage incoming fire, which was its primary function. The basic principle of the weapon allowed for near-luminal speeds, which meant the weapon could engage targets at almost all visual ranges and with flaless speed and precision.
The Raider was also fitted with an MD8 Integrated LASER Countermeasure System, which consisted of a combined LASER Rangefinder (LR), LASER Warning Receiver (LWR), and LASER Self-Defense Weapon (LSDW). The MD8 was arranged with the majority of its components below the armour, in order to protect them from enemy fire. In addition to a rangefinder and a warning reciever alerting the crew if the Raider was being targeted, it fired a high-powered LASER to directly attack an enemy weapon's optics and gunner.
Arranged in a vertical fashion between the two internal ammunition stays of the turret bustle, the MD8 used a multi-wavelength beam splitter in front of a high powered LASER emitter, which allowed for a single high powered beam to be split into multiple beams each with their own coded wavelength. Above the LASER and beam splitter sat a nitrogen filled chamber that could be raised and lowered as the battle permitted, to protect the somewhat sensitive unit from hostile fire. At the top of this chamber was a cylinder of clear bullet and plasma resistant material, consisting of layers of polycarbonate laminate with an energy ablative and plasma refracting coating. This allowed for some protection from battlefield hazards without interfering with the suite’s effectiveness. Sitting in this chamber was a conical reflector, designed to allow several split beams to be directed at multiple targets up to the LSDW’s highest power. This arrangement allowed for multiple sources to not only be targeted (for direction of VARs) or to neutralise several enemy vehicles simultaneously. In this arrangement the ILCS did not require a high rate slewing assembly as the rate of traverse could be nearly at the speed of light, depending on the number of beams in use.
==Engine==
The Raider's primary engine setup consisted of a conventional diesel engine operation in tandem with a plasma reactor similar in concept to those used by the Covenant. Under normal conditions both these engines would operate together; though sometimes they were used individually also. The XVM-90C Fusion Reactor, which produced a large amount of excess thermal energy, was less stealthy in this respect as well as louder than the diesel engine, which was equipped with advanced thermal and sonic suppressors. it did, however, produce a much higher amount of energy, and was therefore used mainly in situations where stealth was not necessary. The diesel engine could provide the tank with a more rapid 'sprint' of speed than the reactor, as well as being more stealthy, and was therefore used for silent operations.
The power pack, consisting of the two engines and transmission system, was configured for ease of maintenance and could be replaced within 45 minutes in the field. The 135° V16 engine generated 1440W or 1,931 horsepower, and was designed by the UNSC Army as a turbocharged air-cooled diesel engine originally intended for the second generation Scorpion. The 135° overhead 'V' layout made the engine nearly perfectly balanced with 8 cylinders opposing 8 cylinders in fluid movement, reducing both noise and vibration, both common problems with alternative diesel engines. Using conical combustion chambers allowed for the highest torque and brake horsepower of any engine in a UNSC tank yet; the engine's moving parts were constructed mainly from carbon nanofibre or titanium.
The automatic transmission had a hydrostatic transmission unit with five forward and two reverse gears. The final drive gears were epicyclic in design and provided higher torque at lower RPM than a traditional gear arrangement, as well as increasing the engine's fuel economy. The final drives were also connected by a cross-shaft which gave higher power efficiency in turning manoeuvres by transferring the power regenerated at the inner track during a turn to the outer track. The track system of the Raider was a dual pin metallic track with rubberised buffer/traction pads, using a pair of integrated locking pins. Each section of track contained several slip rings with a triangular inner cutout. This cutout helped align and retain the pins better over rough terrain while allowing for ease of replacement, without compromising strength. The rubberised traction pads of the Raider were much like the treads on a rubber tire and assisted not only in on road travel, but also over rocky terrain or wet ground.
The Raider’s tracks consisted of four independently articulated bogies; these could run in several settings depending on the terrain, conditions and commander's preference, the ultimate result being the maximum possibly stability for the vehicle. The running gear of each bogie consisted of six dual rubber lined road wheels, with three return rollers on each side and connector type tracks. The suspension was mounted on the under frame and not on the side frames, so the suspension was separated from the hull. A result of using a decoupled suspension was that the internal noise level is as low as 85 decibels, which is sufficiently low to meet civilian vehicle noise requirements. The decoupled suspension also provided a spaced outer layer which gave improved protection against mines and improvised explosive devices. This allowed the Raider to withstand a 7kg TNT explosion under a track without significant loss of mobility or the crew. There were disc type brakes on each of the final drives, integrated by the transmission retarder.
The Raider's decoupled suspension system was a combined nitrogen gas spring and hydraulic dampening system. For weapon firing, an automated series of valves on the nitrogen gas system were closed to provide a firmer hydraulic suspension system meaning better accuracy. Once the main weapon was discharged the nitrogen gas system was reinstated into the vehicle suspension system, restoring it to full capability.
==Systems==
===Stealth Measures===
Although not specifically a 'stealth tank', the Raider did make use of several advanced detection reduction methods that rendered it almost invisible on even the Covenant's sophisticated RADAR-based sensors. The hull's outer coat was a matte rubberised polymer spray coating to decrease its UV reflections and to distort LADAR and laser rangefinders. This radar absorbent material (RAM) both heavily reduced its RADAR cross-section, preventing it from being detected, and affecting the enemy's accuracy if it was discovered. It also was shown to decrease the power of direct laser sources for the purposes of target illumination, increasing the tank's survivability. Variable thermostatic circuits maintained the tank's exterior temperature in accordance with that of its surroundings, rendering it undetectable on thermal imaging. In addition, the tank's covered air intake was located near its diesel engine exhaust, the two effectively cancelling each other out when the Raider ran in its second engine. The tank also featured a dual power system which enabled a choice of full operational capacity or reduced capacity and increased stealth abilities. The Raider's hull was also mainly flat surfaces and sharp edges, reducing the likelihood of radar bounce-back towards the emitter. The Raider made extensive use of heat sinks, exhaust baffles and other passive stealth measures to further reduce its detectability. The result was a vehicle that, when stationary, was indistinguishable from its surroundings on Covenant sensors, and when mobile could be mistaken for a small animal. The tank's communications, electronics and sensor systems were all optimised for low probability of intercept (LPI) meaning the chance of its detection through these methods was minimal.
===Fire Control===
The Raider was equipped with the VISTA all weather vision system, which provided nearly unlimited sight under difficulty visibility conditions such as dark nights, hard rain, fog, heavy dust etc, without the need for active illumination. The system combined dual-band visual Imaging Infrared TV (I2CCD or Image Intensifying Charge-coupled device) and thermal IR sensor head covering 40x30 degrees. A special algorithm combined the two images into an enhanced picture. Colour coding was used to highlight specific objects as selected by the commander, or as detected by analysis system which instantly picked up any targets. The gun's ballistic solution was calculated using a wide range of sources including a laser rangefinder, crosswind sensor, data concerning performance and flight characteristics of each specific type of round, tank-specific boresight alignment data, ammunition temperature, air temperature, barometric pressure, a muzzle reference system (MRS) that determine and compensated for barrel droop at the muzzle due to gravitational pull and barrel heating due to firing or sunlight, and target speed determined by tracking rate tachometers in the Gunner's or Commander's controls handles. All of these factors are computed into a ballistic solution and updated 30 times per second.
The hybrid turret and gun control system consisted of a hydraulic elevation drive and an electric traverse drive. The line of sight stabilisation in more than just elevation and azimuth provided high hit probability for stationary and on the move engagements against both stationary and moving targets. The system had four modes of operation: stabilised mode with the gun axis slaved to the line of sight, slaved mode where the gunner's line of sight was slaved to the gun axis, a non stabilised mode and back-up mode with manual operation for emergency use. A fixed gunner's stabilised VISTA sight with laser rangefinder was assisted by a digital fire control computer to form the primary fire control functions for the Raider. The digital fire control computer downloaded data from the tank's meteorological and wind sensors, together with the tank attitude, barrel wear characteristics, ammunition selected and target data (as well as previously mentioned ballistic solution data) then calculated the fire control algorithms and was used to control the gun, the sighting systems and the laser rangefinder to ensure an accurate shot. Though not revolutionary, the system was effective and battle proven.
The commander's station on the right of the turret was equipped with the panoramic stabilised VISTA sight and a monitor displaying the thermal/EO image from the gunner's sight. The commander's sight, mounted on the centerline of the turret, had a 360° traverse and an elevation range from -10° to +60°. A separated laser rangefinder was also used and the computer was cable of tracking 'pre-tagged' targets for the gunner while the commanders sight was no longer designating. Both the Gunner's and Commander's sights were behind a 45° angled reflective polymer cover, which prevented enemy vehicles from attempting to blind the sights on the vehicle by means of laser or other means.
==Quotes==
==Trivia==
*The appearance of the Raider is based on early concept ideas of the Grizzly Tank from Halo Wars, in which it only mounted a single 120mm Cannon.
*The main quote for this article was kindly provided by SPARTAN-118.
Category:AAO Vehicles
Category:UNSC
Category:UNSC Vehicles