Spaced armour

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Armour with plates spaced a distance apart

title: "Spaced armour" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["vehicle-armour"] description: "Armour with plates spaced a distance apart" topic_path: "general/vehicle-armour" source: "https://en.wikipedia.org/wiki/Spaced_armour" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Armour with plates spaced a distance apart ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/f9/Pz-IVG-latrun-4.jpg" caption="Spaced armour around the turret of a [[PzKpfw IV"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/5/52/Bundesarchiv_Bild_101I-219-0595-23,_Russland-Mitte-Süd,_Panzer_III.jpg" caption="PzKpfw III Ausf. M]] protecting the hull and turret, June 1943"] ::

Armour with two or more plates spaced a distance apart falls under the category of spaced armour. Spaced armour can be sloped or unsloped. When sloped, it reduces the penetrating power of bullets and solid shot, as after penetrating each plate projectiles tend to tumble, deflect, deform, or disintegrate; spaced armour that is not sloped is generally designed to provide protection from explosive projectiles, which detonate before reaching the primary armour. Spaced armour is used on military vehicles such as tanks and combat bulldozers. In a less common application, it is used in some spacecraft that use Whipple shields.

Against kinetic penetrators

Tank spaced armour has been fielded since the First World War, when it was fitted to the French Schneider CA1 and Saint-Chamond tanks. The late variants of Panzer III had frontal spaced armour: a 20 mm thick face-hardened steel layer in front of the 50 mm thick main armour. Impacted projectiles were physically damaged by the 20 mm plate, so the main armour could withstand much greater hits. Due to lack of materials, German industry eventually switched to Rolled Homogeneous Armour (RHA), which is less effective and due to the slower production process, the technique was not widespread on German tanks.

Many World War II–era German tanks used armoured skirts (Schürzen) to make their thinner side-armour more resistant to anti-tank rifles, contrary to popular belief that the German Schürzen were designed against shaped charge projectiles. The common Russian PTRS rifles could penetrate 35 to of armor at common combat ranges, whereas many German tanks only had 30 mm of armor on their sides. The skirts thus added 8 mm of additional thickness to make up the difference, and could theoretically cause the round to tumble, improving protection against those weapons. Nevertheless these rifles continued to be useful throughout the war.

Postwar analysis of spaced armour at the US Aberdeen Proving Grounds found spaced armour to be ineffective if the layers are of roughly equal thickness. Numerous trials invariably showed that combinations of multiple plates provided "considerably less protection than a single solid plate of the same total thickness". This is because the midsection of plates provides more resistance to penetration than the front and rear surfaces, and thus having a thicker plate offers better performance. Instead additional layers of armour should be the thinnest required to obtain the possibility of fracturing the projectile, which has the best results in improving protection, though this effect was not consistent and could be mitigated by improved projectile design. Projectiles impacting against sloped spaced armour at greater standoff ranges could also result in the projectile turning to impact the second plate at a more perpendicular angle, making the added armour worse than nothing. This is because a projectile penetrating a plate is deflected towards the normal, an effect that could ruin an armour scheme.

Though spaced armour appeared in some tanks like the Leopard 1 and the Merkava, the armour scheme was not considered to offer sufficiently better protection against armour-piercing projectiles to justify the increased complication they posed, and thus their use on post-war tanks was limited and eventually superseded by more effective composite armour.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/4e/Merkava-1-batey-haosef-2.jpg" caption="Storage spaces within the spaced armour on a Merkava MBT"] ::

Against high explosive anti-tank rounds

Most of the Cold War spaced armour was designed against medium-to-low caliber kinetic munitions, (e.g. 30 mm autocannon and 76 mm HESH rounds), especially vehicle side skirts. Most of them were made of RHA plates (Centurion), or thick reinforced rubbers (T-72), and worked in the same way as did WWII-era ones. Some WWII armoured vehicles used nets of wooden logs at a certain distance from the hull as makeshift spaced armour to protect the vehicle from magnetic mines, thrown shaped charges and grenades, and occasionally suicidal methods (e.g. the Japanese lunge mine). This method occurred on US M4 Sherman and Soviet T-34 medium tanks among others.

The idea is that this thin layer of armour detonates explosive warheads prematurely. Such techniques were effective in warships against armour piercing shells with short fuzes.

To increase effectiveness of skirts against HEAT weapons early T-64s had "gill" skirts. It contained a few short skirts on the side of the vehicle which are opened in open terrain at an angle of between 30–45°, increasing the space between the armour and the plate. It was effective (mass-to-efficiency ratio), but easily detached from the vehicle so it did not spread widely.

Military researchers tried to increase the efficiency of armour by changing the used materials and varying the armour layout, leading to more complex composite armour, which can incorporate empty spaces.

Commented out. Most of this material belongs better in the composite armour article. Checking the references finds virtually none refer to "composite spaced armour". Googling finds no reference to this phrase.

Composite spaced armour

Multilayer spaced armour, which also use special materials, are a transition to composite armour, most of the latter are also partially spaced armour. ::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/b5/T-55AM_in_the_Kubinka_Museum.jpg" caption="BDD armour on a T-55AM"] ::

In the case of the Leopard 1A3 and later variants, the outer layer of spaced armour was hardened steel and the space was filled by elastomer, thus the effectiveness of the shattering effect of the outer layer against APFSDS was outstanding, and the protection against early HEAT warheads was increased, too. The BDD add-on armour of T-55 and T-62 series based on the same effect, but it had multiple layers within elastomer, therefore it roughly doubled the frontal protection of these tanks against APDS and HEAT weapons, and made the areas of add-on immune to HESH rounds. In T-64 and early T-72 (up to T-72M1) and T-80 (to mid T-80A) used stekloplastik (a special military-grade dense glass-fiber reinforced pressured plastic) as filling in the frontal upper glacis spaced armour. This plastic was effective in lowering the concentration of the jet of shaped charges and in destabilizing kinetic penetrators.

Hardened steel plates have become commonplace for the outer part of spaced armour from the 1980s, not only on tanks but also on APCs and IFVs. With this add-on armour, even the APC's thin armour is sufficient against kinetic bullets of 12.7 mm (Stryker and BTR-80 upgrades) and 14.5 mm (Bradley, BMP-3) and also provides some protection against IEDs.

The increase in the number of layers in spaced armour increases the physical damage and destabilization of jets and kinetic penetrators, so it is common in more modern armour to use successive layers alternating between softer (air, aluminium or plastic) and harder (RHA, SHS) layers. With multiple layers the likelihood of a bounce in case of kinetic projectiles is also increased. Thus, later T-72B and T-90 armour used seven-layered spaced armour (with hardened steel plates) to achieve much stronger protection at a cost of minimal weight increases.

The more advanced late Cold War tanks were given multi-layer skirts (Leopard 2), in which passive (or reactive) effects significantly reduced the effectiveness of HEAT ammunition. At the same time, these elements are already heavy and have considerable thickness, which increases the size and weight of the vehicle and make maintenance difficult. Russian and some Western tanks carry explosive-reactive armour blocks to increase the effectiveness of spaced armour (particularly in the case of side skirts, e.g. TUSK and T-90), and main frontal armour.

Almost all modern Western and Japanese and most Soviet tanks used some kind of spaced armour on the fronts and sides. Side panels of superstructures usually contain fuel, batteries and other less vital elements or munition of secondary weapons, because they also reduce the effectiveness of penetrating projectiles. In the most important areas (frontal armour and sides of turret) the cavity of spaced armour contains composite panels. From the 1980s, most Western tanks have composite armour blocks on the frontal part of the skirts, made of hardened steel or NERA armour (non-explosive-reactive armour, known as "Burlinghton armour"

https://www.defencetalk.com/military/forums/t/non-explosive-reactive-armour-nera.9690/ https://www.researchgate.net/publication/318368846_Future_Armour_Materials_and_Technologies_for_Combat_Platforms/figures?lo=1 https://defensepoliticsasia.com/nera-understanding-non-explosive-reactive-armour/ https://tankandafvnews.com/2016/02/23/from-the-vault-chieftain-articles-and-documents/ ). Most modern MBTs (e.g. T-72B, Leopard 2, M1, Type 10, K2, T-90, Type96) have NERA armour in their spaced armour which supplement the inner ceramic armour and spall liners in some cases. In contrast, Soviet tanks were initially made with ceramic (corundum or silicate) inserts (T-64A, T-72A, T-72M1, T-80) and NERA-style inserts spread in the upgraded versions of their vehicles later (T-72B, T-80A, T-72BU). More detail in composite armour.

Currently, composite spaced armour with hardened steel outer layer (often filled with NERA or ceramic inserts) are becoming more common on most advanced light battle tanks (ZTQ-15) and IFVs (Namer, Puma).

Materials

As designs became more specialized, more and more materials were used. The most important are:

Elastomers

Some modern main battle tanks (MBTs) and IFVs carry rubber or steel (hardened in some cases) skirts to protect their relatively fragile suspension and lower side armour and lower glacis, often combining the two. Some elastomer fillings (e.g. M551's floating cells and screens, T-72B's radiation protection layer) behave like spaced armour, where the elastic layer effectively lowers the concentration of the jet of HEAT warheads. Leopard 1A3s and 1A4s and the add-on armour of T-55s and T-62s use dense polystyrene filling to increase the effectiveness of spaced armour. The early second generation Russian MBTs use dense glass-fibre reinforced pressured plastic as filling in the frontal upper glacis spaced armour, which is even more effective than the pure elastomer.

NERA armour also use elastomers pressed between two or three sheets of steel, or aluminium layers; it acts as ERA armour with lesser effectiveness, but is not destroyed during operation, so it can hold multiple hits in the same place. Most of the modern MBTs use some NERA layer within their spaced armour, or as an outer layer.

Hardened steel

Whereas normal armour must compromise between hardness and ductility, spaced armour can be constructed from plates with differing material properties to increase effectiveness against kinetic energy penetrators. Most of the Cold War and modern spaced armours use rolled homogeneous armour as the inner layer and a thin (10–30 mm) face-hardened, semi-hardened steel plate as the outer layer. The thin but very hard outer layer acts as a burster and shatter plate, which allows the main armour to be designed much thinner with the same protection level. The most advanced designs use triple- or high-hardened steel. In some cases aluminium is added to hardened steel armour as a softer inter-layer to destabilise the projectiles and HEAT jets by density changes.

The Leopard 2 uses a slanted first armour stage (disturber), a specially hardened second stage (disrupter) and a softer, high ductility third stage (absorber). The disturber is designed to either entirely deflect or manipulate the direction of incoming kinetic energy penetrators. If penetration does occur, the projectile is then shattered and fragmented when striking the disrupter. Assuming the first two stages work properly, the absorber stage captures spalling and fragments.

Others

Some armoured fighting vehicles use the cavity of their spaced armour as fuel tanks or storage spaces, and warships used them as coal or oil bunkers, and rooms for non-vital components (e.g. washing rooms, food storage). The materials filling these spaces could further slow down the penetrating projectile, increasing the protection. Modern AFVs spaced armour contain special fillings forming composite armours.

Spacecraft

The Whipple shield uses the principle of spaced armour to protect spacecraft from the impacts of very fast micrometeoroids. The impact with the first wall melts or breaks up the incoming particle, causing fragments to be spread over a wider area when striking the subsequent walls.

References

References

  1. Thomas, Steven. (16 July 2003}}{{self-published source). "Why were Schürzen introduced in WW2?".
  2. Hughes, Matthew. (2000). "The Panther Tank". Spellmount.
  3. (4 November 2016). "The PTRS 41 and Other and Russian Anti-Tank Rifles".
  4. A. Hurlich. (November 1950). "Spaced Armor".
  5. Nathan Okun. (2008). "Multi-Plate Armor Versus Single Solid Plates: Pros And Cons For Each".
  6. Ogorkiewicz, Richard M. (1991). "Technology of tanks".
  7. "The most misunderstood weapon in the world: Mythbusting HEAT warheads and their countermeasures".
  8. WILEY-VCH Verlag GmbH, D-69451 Weinheim (1999) – Propellants, Explosives, Pyrotechnics 24 – Effectiveness Factors for Explosive Reactive Armour Systems. p. 71
  9. Warford, James. (2002). "Ilich's Eyebrows". Armor.
  10. "Основной боевой танк Т-80У "Объект 219АС"".
  11. "Leopard-2A0-A4 armor protection estimation".
  12. Tankandafvnews. (23 February 2016). "From the Vault: Chieftain Articles and Documents".
  13. Sukumar, G.. (2017). "Future Armour Materials and Technologies for Combat Platforms". Defence Science Journal.
  14. "ZTQ Light Tank".
  15. "Puma AIFV Tracked Armoured Infantry Fighting Vehicle".

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