Armour is one of the three key aspects of tank design to ensure tank survivability. For some countries it is more important to heavily armour their vehicles, which then reduces the vehicles mobility (British Army) and then others countries (The German Army) prefer less armour to increase the vehicles mobility.

The more simplistic forms of armour

Sloped Armour

Sloped Armour was firstly mass used by the Russians on the T-34 in World War II and then by the Germans on the Panther. Rather than having a vertical 90° surface, by changing its angle to an almost horizontal one of 45°, the thickness of the armour is double of that whilst at a vertical angle. Its second main purpose is that an incoming round does not have a flat surface to strike against and is deflected off the vehicle.

Appliqué Armour

Appliqué Armour is not a type of armour system, but simply a term used when additional plates of armour, be it metal or ceramics are added to the existing armour or hull and turret surface.

Stand Off Armour

Stand Off Armour is a very simplistic and effective type of armour against older HEAT projectiles such as the RPG-7. Stand off simply means an additional surface or object is placed around the vehicle, creating a gap/space between it and the skin of the vehicle. The most common type's are Spaced armour, Passive and Cage AKA Bar.

Spaced Armour - is a form of stand-off armour and used by countries that generally prioritise speed over armour in the vehicles survivability as its lighter. Simply put, its increasing the distance between the skin of the vehicle and the fighting compartment. It's designed so that the distance causes the round to tumble or deflect. Its commonly used to defeat HEAT projectiles by increasing the distance between the initial impact and the distance the jet of metal released by the HEAT projectile has to travel to penetrate the crew compartment/explosive materials.

Cage Armour AKA BAR or Slat - has to be the most cost effective type of armour. It is the simplest version of stand-off armour. Whilst there is no serious threat to NATO forces of armoured vehicle's fighting other armoured vehicle's, their most common threat is from HEAT projectiles, notably the RPG-7, a weapon that is cheap and highly accessible. Like Spaced Armour, it works by holding off the HEAT projectile from the skin of the vehicle, so that when it releases its jet of metal, there is an unreachable distance for it to travel to the skin of the vehicle. However, more modern HEAT projectiles, which are very short in supply, such as the RPG-29 can defeat cage armour.

Perforated armor plates - are another form of stand off armour. Simply put, they are two plates of steel with a space between them, which are attached to a vertical surface and are full of holes. These holes are cut at angles such as 45° so that an incoming projectile is deflected when passing through it to a new angle rather than that of its original path and to take out its energy. Some types the gaps are filled with foam. This system is on the hull of the Leopard 2.

Passive Armour - is another form of stand-off armour. Like spaced armour, It comprises of a rigid enclosure (box/module) but instead of containing a couple of plates of different materials, it is filled with hollow microspheres made of a material having a density greater than 7 g/cm3 to 10 g/cm3. It works like spaced armour, in that by having an angled front it distorts the path of the copper jet from a HEAT projectile and then is again distorted by the microspheres. An example of Passive Armour is the wedge shaped MEXAS system on the Leopard 2 (A5 and upwards).

The more sophisticated armour systems

Laminated Armour - Laminated armour was developed primarily by the UK. It consists of 2 flat layers of steel armour plate (heat treated to increase hardness) with a layer of ceramics/fibreglass or other harden/dense material in between both plates. This armour is highly effective against all types of weapons. Vehicles with laminated armour can be identified by their flat/slab sides, such as the M1A1 with it's frontal DU mesh between both plates.

Composite Armour - Composite armour is the use of a number of different ceramic tiles (inorganic non-metallic materials) and other hardened/dense materials and is often assumed that Chobham armour is the only type of composite armour. This is incorrect.

The use of these materials in combination offers a greater level of protection compared to steel, as they are normally more dense and harder to penetrate. Composite armour can vary in so much as to the materials used in the combination and the number of them, which varies the effectiveness of the level of protection they offer.

Composite armour can be deployed or rather fixed to the vehicle in 3 ways:

1. The composite core is fixed to the tanks metal skin and then an outer plate cover of steel is then fixed on top of the core to cover it or the outer steel is moulded around the core to cover it.

2. Modular, Ceramic tiles or other materials are vertically slotted in to place in a rigid enclosure known as a module. This module is then bolted on to the external steel skin of the vehicle. It's main advantage is that the ceramic tiles in the module are quicker to access than that of the encased core of composite/laminate, therefore making it easier to up-grade with newer ceramics and replace after being damaged, as the module can be easily un-bolted and replaced. Its currently used on the Leclerc and Merkava Mk4.

3. The British Tank Research Centre developed a new bonding process and matrix for a superior combination of tiles they chose, which was called Chobham. The new bonding process and matrix further increases the hardness and resistance of those tiles by keeping them under a constant compression, which  increases the number of times the armour can be repeatedly hit before failing, which was demonstrated during the 2003 Operation Telic when a stranded CR2 was struck repeatedly by shaped charged RPG-7's and a MILAN. The CR2 uses a new optimum combination of tiles and is called either Chobham Mk2 or Dorchester. The bonding process and matrix was shared only with the US, who used it on the Abrams with a different ceramic mix and was called "Burlington". It was not shared with Germany to use on the Leopard 2 series. It is used to primarily shatter Kinetic Energy penetrator’s and secondly defeat HEAT rounds (shaped head charges).

Reactive Armour

Explosive Reactive Armour - is also another very common form of armour and a lot simpler in its design. Almost like laminate armour, a layer of explosive is sandwiched between two metal plates. When the outer plate is struck, the explosive then blows the metal plate outwards into the incoming projectile, destroying it or forcing it into another direction away from the vehicle. To defeat more modern penetrators, the layer of steel and explosive are made thicker and heavier.

The main downfall of ERA is that when it has exploded it leaves an un-protected area of the vehicles surface, which can then be struck again, and defeat the vehicle. To try to minimise the exposed area, reactive armour is made into blocks the size of bricks, which it’s commonly referred too, rather than a large surface.

ERA proves susceptible to what are called “tandem charged weapons”. These are normally handheld missiles, which have the addition of a second shaped charge set further back in the missile. The first shaped charge triggers the ERA brick and then the second shaped charge impacts on the bare skin of the vehicle where the ERA brick was, penetrating the tank and destroying it. Such missile systems include the Javelin and RPG-29.

Non-Explosive Reactive Armour - AKA NERA, has seen the explosive layer replaced with an inert layer (possibly rubber) between two metal plates. The KE of the copper jet from a shaped charge is then absorbed by the inert layer, which forces the plates in opposite directions, interacting with the copper jet and disturbing its horizontal path.

Electric Reactive Armour - passes an electric current through the incoming projectile absorbing its energy or destroying it. This Type of armour is in development in the UK and other EU countries.