Tank armor is made from layers of steel, ceramic, and other materials arranged in a composite sandwich. The earliest tanks used simple steel plate, but modern main battle tanks like the M1 Abrams, Leopard 2, and Challenger 2 combine rolled steel, ceramic tiles, rubber or polymer sheets, and sometimes depleted uranium into armor arrays that can resist penetration equivalent to over 150 centimeters of solid steel.
Steel: The Foundation of All Tank Armor
Every tank ever built starts with steel. The standard is called rolled homogeneous armor, or RHA, a low-carbon steel alloy that has remained largely unchanged since World War II. The military specification for this steel (MIL-A-12560) uses two main alloy systems: a manganese-molybdenum-boron blend for thinner plates (under about 1.5 inches) and a nickel-chromium-molybdenum blend for thicker sections. The carbon content is kept deliberately low, around 0.26%, so the plates can still be welded together without cracking.
RHA works because it balances hardness with toughness. It needs to be hard enough to resist a projectile but tough enough not to shatter on impact. A typical RHA plate registers around 33 on the Rockwell C hardness scale, which is hard enough to deform incoming rounds but ductile enough to absorb the energy without fragmenting into deadly shards inside the crew compartment. Improved versions push that hardness up to about 42 Rockwell C while maintaining the minimum toughness requirements.
Early tanks were riveted together from flat plates. This was a serious vulnerability: a direct hit could pop rivets loose and send them bouncing around the interior like bullets. Cast armor solved this by forming entire turrets or hull sections as single pieces with rounded corners that deflect glancing shots. Modern tanks have largely returned to welded construction from rolled plates, which are stronger and more uniform than castings, but now the welds themselves are carefully engineered to avoid weak seams.
Composite Armor: The Ceramic Sandwich
Pure steel armor hit a practical limit by the 1960s. Making it thick enough to stop shaped-charge warheads (the kind used in anti-tank missiles) meant making the tank impossibly heavy. The breakthrough came from the British research facility at Chobham, which developed what’s now generically called composite armor: layers of ceramic material sandwiched between steel plates, with the whole package bound together by ballistic nylon or similar fabrics.
The ceramics used in tank armor are the same ultra-hard materials found in body armor, just scaled up. The most common are alumina (aluminum oxide), silicon carbide, and boron carbide. These materials are far harder than the steel or tungsten in incoming projectiles, which is exactly the point. When a round hits the ceramic layer, the ceramic shatters the tip of the projectile, spreading its energy across a wider area. The ceramic itself breaks apart in a cone-shaped fracture pattern, but by then it has already blunted the threat enough for the steel backing plate to catch whatever remains.
This works because ceramics and metals fail in fundamentally different ways. A metal deforms and stretches. A ceramic is brittle: it pulverizes rather than bending. That brittleness is actually an advantage in armor because the shattering process absorbs enormous energy. The tradeoff is that a ceramic tile, once fractured, offers no protection against a second hit in the same spot. That’s why composite armor arrays use many small tiles rather than one large sheet, limiting the damaged area from any single impact.
Some composite arrays also include titanium plates, aluminum honeycomb structures, or layers of advanced plastics. The exact recipes are closely guarded secrets, and they vary between manufacturers and even between different sections of the same tank. The turret front, which faces the most direct threats, typically gets the heaviest and most complex armor package.
Depleted Uranium and Heavy Metal Inserts
The M1A1HA and later Abrams variants add depleted uranium (DU) mesh or tiles into their composite armor arrays. Depleted uranium is roughly 1.7 times denser than lead. When a penetrating rod strikes a DU layer, the uranium’s extreme density and self-sharpening fracture behavior help it resist and redirect the incoming round. The DU is encased within the armor package and poses no radiation hazard to the crew during normal operation. The Challenger 2 also uses DU-enhanced armor in some configurations. This approach gives the Abrams turret front an estimated protection level around 150 centimeters of RHA equivalent against shaped-charge warheads and roughly 96 centimeters against kinetic dart rounds.
Reactive Armor: Turning the Threat Against Itself
Reactive armor takes a completely different approach. Instead of passively absorbing a hit, it actively disrupts the incoming projectile. The most common type, explosive reactive armor (ERA), consists of small box-shaped modules bolted to the outside of the tank. Each box contains a thin sheet of explosive sandwiched between two metal plates, usually steel.
When a shaped-charge jet from an anti-tank missile burns through the outer plate and detonates the explosive, both plates are blown outward in opposite directions. This sideways motion cuts through the narrow jet of molten metal, breaking it up and dramatically reducing its penetrating power. Russian tanks have used ERA extensively since the 1980s, with the Kontakt-5 system being one of the most widely fielded examples.
The downside of explosive reactive armor is obvious: it detonates. That’s dangerous to nearby infantry and any unprotected equipment. It also only works once per module. Non-explosive reactive armor, or NERA, solves both problems by replacing the explosive filler with a thick layer of rubber or another elastomer. When a projectile strikes a NERA module, the rubber deforms rapidly, pushing the front and back steel plates outward in opposite directions. This “bulging effect” doesn’t destroy the incoming round through explosive force. Instead, the plates grab and bend the long, slender tungsten darts used in modern anti-tank ammunition. Since these darts are made from hard but brittle tungsten alloy, bending them causes them to fracture, breaking a single dangerous penetrator into several less effective fragments. Experiments using X-ray imaging have captured this process directly, showing the steel plates deforming with the rubber and the tungsten rod cracking apart between them.
Many modern tanks use both approaches. The Leopard 2A5, for example, added large wedge-shaped appliqué modules to its turret face, bringing its estimated frontal protection to around 100 centimeters RHA equivalent against kinetic rounds and over 150 centimeters against shaped charges.
Spall Liners: Protecting the Crew From the Inside
Even when armor stops a round from entering the vehicle, the impact can blast fragments of metal off the inner wall of the hull. This is called spalling, and it’s lethal. A spall liner is a sheet of ballistic fabric bonded to the inside surface of the armor, acting as a net to catch those fragments before they reach the crew.
Spall liners are made from the same high-performance fibers used in body armor. The most common materials are aramid fibers (the family that includes Kevlar) and ultra-high molecular weight polyethylene, the same material used in products like Dyneema and Spectra. These fibers have extremely high tensile strength, meaning they resist being torn apart by fast-moving fragments. The liner is typically layered, with multiple sheets of woven or pressed fiber bonded together and then attached to the hull with adhesive, sometimes with a blast-mitigating foam layer between the liner and the steel to absorb additional shock.
How These Layers Work Together
A modern tank’s armor is best understood as a system, not a single material. The outermost layer might be bolt-on reactive armor modules designed to break up incoming warheads before they reach the main armor. Behind that sits the composite array: steel face plates, ceramic tiles or DU inserts, and steel backing plates, all bonded into a unified structure. The innermost layer is the spall liner, catching any fragments that make it through everything else.
Each layer handles a different part of the problem. Reactive armor disrupts the projectile’s shape and momentum. Ceramics shatter and blunt whatever remains. Steel absorbs and contains the residual energy. The spall liner catches debris. No single material could do all of this effectively, which is why every modern tank uses some version of this layered approach. The specific combination varies by nation and threat environment, but the principle is universal: force an incoming round to defeat multiple different materials, each one degrading the threat in a different way, until there’s nothing left to penetrate the crew compartment.