How Explosive Reactive Armor Detonates Itself to Stop an Incoming Anti-Tank Missile

The armor detonates itself. On purpose. When an anti-tank missile strikes a tank equipped with explosive reactive armor, the impact triggers a precisely engineered explosion inside the armor block that disrupts the incoming warhead before it can penetrate the main hull. It is one of the most counterintuitive concepts in military engineering: using an explosion to stop an explosion. And it has saved more tank crews than any other armor technology developed in the past 50 years.

The Shaped Charge Problem

To understand why explosive reactive armor exists, you first need to understand the weapon it was designed to defeat. A shaped charge warhead, the type used in rocket-propelled grenades, anti-tank guided missiles, and many other anti-armor weapons, does not destroy a tank through brute explosive force. Instead, it uses a precisely shaped cone of metal, usually copper, lined inside a conical cavity in the explosive charge. When the explosive detonates, the metal liner collapses inward and forward, forming a superplastic jet of molten copper traveling at approximately 8,000 meters per second, roughly 25 times the speed of sound.

This jet is extraordinarily narrow and focused. It does not blow a hole in armor the way a conventional explosion would. Instead, it punches through steel armor by applying enormous pressure to an incredibly small cross-sectional area at pressures that exceed the yield strength of any armor steel. A modern anti-tank guided missile with a shaped charge warhead can penetrate 800 to 1,000 millimeters of rolled homogeneous armor equivalent, far more than the thickness of any tank's main armor plate.

Traditional steel armor, no matter how thick, struggles against shaped charges because the jet's penetration capability scales with its length and velocity rather than the armor's thickness. Making a tank's armor thick enough to stop a modern shaped charge would make the vehicle too heavy to move. A different approach was needed.

The ERA Sandwich

Explosive reactive armor consists of a deceptively simple structure: two metal plates, typically steel, with a layer of explosive material sandwiched between them. These elements are assembled into modular blocks or "bricks" that are bolted onto the exterior of a tank's hull and turret. Each block is a self-contained reactive element that functions independently.

When a shaped charge jet penetrates the outer steel plate and contacts the explosive layer, the explosive detonates. This detonation propels the two steel plates rapidly outward in opposite directions. The outer plate flies away from the tank, and the inner plate flies inward (but is stopped by the tank's main armor). The key is what happens to the shaped charge jet during this process.

How the Jet Gets Disrupted

The physics of disruption work on two principles. First, the outward-moving steel plates physically intersect the shaped charge jet at an angle. Because the plates are moving laterally, sideways relative to the jet's path, they effectively "swipe" through the jet stream, breaking it into discontinuous segments. A shaped charge jet is devastating precisely because it is a continuous, coherent stream of high-velocity metal. Break that stream into fragments, and each fragment loses penetrating power because it arrives at the main armor independently rather than as part of a sustained, pressure-maintaining jet.

Second, the detonation itself generates a pressure wave that further disrupts the jet's coherence. The explosive gases expand rapidly around the jet, introducing lateral forces that deflect and scatter the jet particles. The combination of plate interference and blast disruption can reduce the penetration of a shaped charge by 50 to 70 percent, enough in many cases to bring the residual penetration within the protective capability of the tank's main armor.

The angle at which the ERA blocks are mounted matters enormously. Blocks mounted at steep angles relative to the incoming threat present more effective plate travel across the jet path, increasing disruption. This is why ERA blocks are typically arranged in a chevron or "V" pattern on tank turrets because the geometry maximizes the lateral plate velocity across the widest range of incoming threat angles.

From Blazer to Kontakt: A Soviet Innovation

The concept of reactive armor was first proposed in the 1960s, but Israel was the first nation to deploy it operationally. During the 1982 Lebanon War, Israeli Magach tanks (modified M48 and M60 Pattons) carried the Blazer ERA system developed by Rafael Advanced Defense Systems. Blazer proved spectacularly effective against the RPG-7 rockets and AT-3 Sagger anti-tank guided missiles used by Syrian and Palestinian forces. Tanks that would have been penetrated by these weapons survived multiple hits, and the psychological impact on anti-tank missile operators, watching their weapons detonate harmlessly against ERA-equipped tanks, was significant.

The Soviet Union watched the Lebanon War closely and recognized both the potential and the vulnerability. Soviet anti-tank doctrine relied heavily on shaped charge weapons. The RPG-7, AT-4 Spigot, AT-5 Spandrel, and AT-6 Spiral were all shaped charge weapons. If their adversaries adopted ERA, Soviet anti-armor capability would be significantly degraded. The Soviets needed their own ERA, and they needed it to be better.

The result was Kontakt-1, fielded in 1985. Kontakt-1 blocks used a more energetic explosive composition than Blazer and were designed for rapid installation on existing Soviet tank fleets, primarily the T-64, T-72, and T-80. A tank could be fitted with a full set of Kontakt-1 blocks in a matter of hours using nothing more than bolts and hand tools. The system provided effective protection against single-warhead shaped charges but shared a limitation with all first-generation ERA: it was ineffective against kinetic energy penetrators like armor-piercing fin-stabilized discarding sabot (APFSDS) rounds fired by tank guns.

Kontakt-5: Stopping Kinetic Rounds

Kontakt-5, introduced in 1986, represented a generational leap. Its explosive composition, with a TNT equivalent of approximately 330 grams per block, was specifically formulated to be sensitive enough to detonate on impact from kinetic energy penetrators, not just shaped charge jets. The thicker steel flyer plates were designed to physically deflect and break APFSDS long-rod penetrators, essentially bending or snapping the tungsten or depleted uranium "dart" as the plates slam into it at high velocity.

This was a breakthrough. Before Kontakt-5, ERA was considered a defense against missiles and rockets only. Kontakt-5 made ERA relevant against the primary anti-tank weapon in the Western arsenal: the 120mm APFSDS round fired by the M1 Abrams, Leopard 2, and Challenger 2 main battle tanks. Western intelligence assessments in the early 1990s indicated that Kontakt-5 could reduce the penetration of contemporary NATO kinetic rounds by 20 to 40 percent, enough to potentially save a T-80U from frontal penetration by weapons that would otherwise kill it.

Relikt: Third-Generation ERA

Russia's current-generation ERA system is Relikt, developed by NII Stali (the Steel Research Institute). Relikt uses a completely redesigned explosive composition and flyer plate geometry that is claimed to be twice as effective as Kontakt-5 against shaped charges and 50 percent more effective against kinetic penetrators. The system works reliably against both low-velocity threats (like RPG warheads) and high-velocity threats (like APFSDS rounds), addressing a limitation of earlier ERA that sometimes failed to detonate against slower-moving projectiles.

Relikt also incorporates improved mounting and arrangement systems that reduce the gap between adjacent blocks, a vulnerability in earlier ERA installations where shaped charge jets could exploit the seams between blocks to penetrate without triggering a reactive element.

The T-90M Proryv, Russia's most modern operational tank, uses Relikt ERA as part of its multi-layered protection system that also includes composite armor, active protection sensors, and the Shtora-1 electro-optical countermeasure system.

The Tandem Warhead Problem

ERA's greatest vulnerability is the tandem warhead, a weapon specifically designed to defeat reactive armor. A tandem warhead carries two shaped charges in sequence. The first charge, called the precursor, is a small shaped charge positioned at the front of the missile. When the missile strikes the ERA block, the precursor detonates the reactive armor element before the main warhead arrives. The main warhead, following milliseconds behind, then strikes armor that has already expended its reactive element and can no longer respond.

The FGM-148 Javelin, the most widely used man-portable anti-tank missile in Western arsenals, uses a tandem warhead specifically designed to defeat ERA. The Javelin attacks in a top-down profile, diving onto the thin roof armor of tanks where ERA coverage is typically minimal or absent, and its tandem warhead neutralizes whatever reactive armor it does encounter. This double threat of top-attack trajectory plus tandem warhead is why the Javelin has proven so effective against ERA-equipped Russian tanks in Ukraine.

Limitations and Infantry Risk

ERA has several inherent limitations beyond the tandem warhead vulnerability. Each ERA block is a one-time-use device. Once it detonates, the spot it protected is bare armor until the block is physically replaced, something that cannot be done in combat. A tank that survives multiple hits may find entire sections of its armor stripped of reactive protection, leaving it vulnerable to subsequent attacks in the same area.

The detonation itself poses a serious risk to dismounted infantry near the tank. When an ERA block explodes, it propels steel plates and fragments outward at high velocity. Infantry soldiers operating within several meters of an ERA-equipped tank can be killed or seriously wounded by the reactive armor detonation even if the incoming missile would not have harmed them directly. This forces tactical compromises. Infantry cannot shelter behind or beside ERA-equipped tanks the way they might with conventionally armored vehicles.

Non-Energetic Reactive Armor (NERA) and Non-Explosive Reactive Armor (NxRA) address the infantry hazard by replacing the explosive layer with inert materials, typically rubber or other elastomeric compounds, that bulge outward when struck, disrupting shaped charge jets through mechanical deformation rather than detonation. NERA is less effective than ERA against the most advanced threats, but it eliminates the fragmentation hazard and can be used in areas where infantry proximity is expected.

ERA in Ukraine: Real-World Performance

The conflict in Ukraine has provided the most extensive real-world test of explosive reactive armor since the technology was invented. Russian tanks, primarily T-72B3s and T-80BVMs equipped with Kontakt-1, Kontakt-5, or Relikt ERA, have faced a saturation of anti-tank weapons including Javelin tandem warheads, NLAW top-attack missiles, drone-dropped munitions, and massive quantities of older RPG-7 and AT-4 variants.

The results have been mixed. ERA has clearly saved tanks from single RPG hits and older anti-tank guided missiles, confirming its effectiveness against the threats it was originally designed to counter. But it has struggled against the volume and diversity of modern anti-armor threats deployed simultaneously. Drone-dropped munitions target the thin roof armor where ERA coverage is sparse. Tandem warheads defeat the reactive elements directly. And the sheer quantity of anti-tank weapons available to Ukrainian forces means that even tanks whose ERA works as designed may face more hits than they have reactive elements to counter.

What Ukraine has demonstrated is that ERA remains a valuable component of tank protection, but it is no longer sufficient as a standalone defense. The future of armored vehicle survivability lies in layered systems that combine ERA with active protection systems (which intercept incoming missiles before they reach the armor), composite armor, cage armor, and electronic countermeasures. ERA will remain part of that layered defense for decades to come, but the era of relying on reactive armor alone is over.