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MITHRIL armour is the name informally given to a composite armour developed in the 2530s at the British tank research centre on Chobham Common, Surrey, England under Project EXCALIBUR. It is considered to be a logical outgrowth of the Chobham armour developed there during the 1960s, combined with salvaged Covenant materials technology. Although the construction details of the MITHRIL armour remain a secret, it has been described as being composed of ceramic tiles encased within a metal matrix and bonded to a backing plate and several elastic layers. Due to the extreme hardness of the ceramics used, they offer superior resistance against shaped charges such as high explosive anti-tank (HEAT) rounds and they shatter kinetic energy penetrators, with even the earliest generations offering a resistance to Covenant plasma weapons that astounded even the design team. Originally designed only for tanks, its extreme versatility against both ballistic and plasma attacks have seen its use expanded into areas such as body armour and warship armour plate.

Protective qualities

Due to the extreme hardness of the ceramics used, they offer superior resistance against a shaped charge jet and they shatter KE penetrators. The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will, within a certain velocity range (the "gap"), not lead to a deeper penetration but destroy the projectile itself instead. Because the ceramic is so brittle, the entrance channel of a shaped charge jet or plasma shot is not smooth — as it would be when penetrating a metal — but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet or shot, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed blast of plasma or molten metal causes still greater irregularities in the ceramic, until in the end it is defeated. The optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection". This mechanism using the blast's own energy against it, has caused some to compare the effects of MITHRIL to those of reactive armour. Should a MITHRIL plate be struck by a laser or particle beam, such as those used in Covenant Beam Rifles, a similar effect is seen as the beam is diffused and broken up by vapourised ceramic.

The effectiveness of MITHRIL armour was demonstrated in live-fire tests prior to development, where no tank was destroyed by HEAT, HESH, or KE penetrator shots except with massed, overwhelming fire at close range. As of December 2571, few MITHRIL armour-protected tanks have been defeated by enemy fire in combat; even during the First and Second Great Wars, despite the huge death tolls, MITHRIL-armoured UNSC tanks were able to score incredibly lopsided kill ratios against Covenant armour, the average being three hundred Wraiths to one M808B Scorpion Main Battle Tank.


The MITHRIL tiles have a "multiple hit capability" problem in that they cannot sustain successive impacts without quickly losing much of their protective value. To minimise the effects of this the tiles are made as small as possible, but the matrix elements have a minimal practical thickness of about 2.5 centimetres, and the ratio of coverage provided by tiles would become unfavourable, placing a practical limit at a diameter of about ten centimetres. The small hexagonal or square ceramic tiles are encased within the matrix either by isostatically pressing them into the heated matrix, or by gluing them with an epoxy resin. Holding the tiles under constant compression by their matrix greatly improves their resistance to kinetic penetrators, which is difficult to achieve when using glues, however, which also have the disadvantage of possibly being melted by intensely hot plasma impacts.

The matrix has to be backed by a plate, both to reinforce the ceramic tiles from behind and to prevent deformation of the metal matrix by a kinetic impact. This is typically Titanium-A in UNSC vehicles. This assembly is again attached to elastic layers. These absorb impacts somewhat, but their main function is to prolong the service life of the composite matrix by protecting it against the extreme vibrations caused by high-velocity impacts. Several assemblies can be stacked, depending on the available space; this way the armour can be made of a modular nature, adaptable to the tactical situation. The thickness of a typical assemblage is between five and six centimetres. The relative interface defeat component of the protective value of a ceramic is much larger than for steel armour. Using a number of thinner matrices again enlarges that component for the entire armour package, an effect analogous to the use of alternate layers of high hardness and softer steel.

The backing plate reflects the impact energy back to the ceramic tile in a wider cone. This dissipates the energy, limiting the cracking of the ceramic, but also means a more extended area is damaged. Spalling caused by the reflected energy can be partially prevented by a malleable, thin graphite layer on the face of the ceramic absorbing the energy without making it strongly rebound again as a metal face plate would. Should this fail, a layer of non-Newtonian gel is used in most modern MITHRIL-armoured vehicles to catch the spalling before it can enter the crew compartment.

Tiles under compression suffer far less from impacts; in their case it can be advantageous to have a metal face plate bringing the tile also under perpendicular compression. The confined ceramic tile then reinforces the metal face plate.

The whole is placed within the shell formed by the outer and inner wall of the vehicle's hull, the inner wall being the thicker, which is bolted on to the vehicle's Titanium chassis or airframe. Both walls are typically of Titanium-A, and maybe coated with a number of laminates such as Boron Carbide to improve resistance to penetration and heat, as well as Shear-Thickening Liquids of a similar composition to those found in the UNSCDF Ground Combat Uniform, and infrared- and radar-resistant paint.


The most recent developments in the field have resulted in MITHRIL ceramics approximately one hundred times as effective as a steel plate of equal weight. MITHRIL makes use of carbon nanotubes to improve toughness even further. This results in a material that is believed to have an equivalent Mohs hardness of 12 (harder than diamond), and despite its extremely high Young's modulus, its high thermal conductivity means that it is resistant to thermal and impulse shock effects.

The backing plate can be made from titanium. A deformable composite backing plate can combine the function of a metal backing plate and an elastic layer.

Development and application

Developed under Project EXCALIBUR during the 2530s due to the war with the Covenant, MITHRIL was the UNSC's response to the Covenant plasma and particle weapons, which simply blasted straight through the UNSC's best fiftieth-generation Chobham and Titanium-A armour. Developed on Chobham Common in Surrey in England, UNSC scientists combined existing Chobham with captured Covenant materials, creating an incredibly tough ceramic that was poetically christened MITHRIL for its great strength. Tests using captured Covenant weapons revealed that it would take multiple heavy fire at close range from even Wraith plasma mortars to blast through the armour. Even the UNSC's best current M931B2 "Javelin" APFSDS rounds from other Scorpion tanks were unable to penetrate the front and side armour (even at close ranges) of tanks armoured thusly during tests, and in an incident in which another Scorpion tried to destroy a tank that had become stuck in mud and had to be abandoned. As of December 2575, few MITHRIL armour-protected tanks have been defeated by enemy fire in combat; even during the First and Second Great Wars, despite the huge death tolls, MITHRIL-armoured UNSC tanks were able to score incredibly lopsided kill ratios against Covenant armour, the average being three hundred Wraiths to one M808B Scorpion Main Battle Tank.

Originally purely designed to armour ground vehicles, the low weight of the material quickly meant that it became used in the UNSC's M52B Body Armour, designed in the same decade, which provided superior resistance to Covenant plasma compared to the earlier M51A Ballistic Assault Vest. It also found use in armouring aircraft, and after it was found that barely two metres of MITHRIL was enough to stop a barrage of twelve plasma torpedoes, proposals were made to incorporate it into warship armour. However, the cost of creating enough MITHRIL for an entire fleet of ships was deemed too high, although with improved methods, this plan came to fruition in the latter half of the War of Vengeance, with ships such as the Invincible- and King Arthur- classes of arsenal ship carrying metres of MITHRIL armour plate on their hulls.

Behind the Scenes

The article's name was taken from the material in Tolkien's The Lord of the Rings, of which the creator has been a fan for many years.