An explosively formed penetrator, or EFP, is a type of explosive weapon that uses a detonation to reshape a metal disc into a high-velocity slug capable of punching through armored vehicles. Unlike conventional bombs that scatter fragmentation in all directions, an EFP focuses nearly all of its destructive energy into a single point, launching a solid metal projectile at speeds exceeding five times the speed of sound.
How an EFP Works
The basic design is deceptively simple: a cylinder packed with explosives, capped on one end with a shallow metal dish called a liner. When the explosive detonates, the force hits the liner and drives it inward. In a fraction of a second, the dish collapses, folds forward, and stretches into an aerodynamic slug, sometimes described as looking like a stubby metal rod or a rounded bullet. This projectile then flies toward its target at roughly 5,000 meters per second.
The formation happens in three distinct phases. First, the explosive force impacts the liner and accelerates it. Then the liner collapses inward toward the center axis. Finally, it stretches into its elongated penetrator shape. The entire process takes only milliseconds. The result is a dense, fast-moving chunk of metal that carries enormous kinetic energy concentrated on a very small area.
This principle, sometimes called the Misnay-Schardin effect, describes how a flat explosive charge can fling a metal plate outward as a focused projectile. It’s related to, but distinct from, the more familiar shaped charge used in anti-tank rockets since World War II.
EFPs vs. Traditional Shaped Charges
Shaped charges, the kind found in older anti-tank weapons, work by collapsing a cone-shaped metal liner into an extremely thin, fast jet of molten metal. That jet can punch deep into armor but only at close range, and it loses effectiveness rapidly over distance. Shaped charges use a low-mass jet at very high speed.
EFPs take the opposite approach: they use a higher-mass projectile at a somewhat lower speed. The tradeoff is that an EFP doesn’t penetrate as deeply as a shaped charge at point-blank range, but it remains lethal at much greater distances. A conventional shaped charge needs to detonate within a specific standoff distance from its target. An EFP can be effective from dozens or even hundreds of meters away, because the solid slug holds its shape in flight rather than dispersing like a thin metal jet.
What the Liner Is Made Of
The metal liner is the heart of the weapon. Copper is the most common material, chosen for its combination of density and ability to deform without shattering. In improvised versions found in conflict zones, copper plates roughly a quarter inch thick have been typical. Steel cones are also used, sometimes machined on a lathe and pressed into the casing.
In more advanced military applications, tantalum and tantalum-tungsten alloys are considered the top candidates for EFP liners. These metals offer higher density, extremely high melting points, and excellent ability to stretch and reshape under the violent forces of detonation. Iron liners have also been studied, though they behave differently at the microscopic level during formation. The choice of liner material directly affects how well the slug holds together in flight and how deeply it penetrates armor on impact.
Penetration and Destructive Capability
An EFP’s penetration is typically measured against rolled homogeneous armor, the standard steel used to rate military protection. In controlled experiments, advanced double-layer shaped charge designs have produced EFPs capable of punching through 80 millimeters of this armor plate, leaving entry holes over 50 millimeters wide. Optimized designs that stretch the slug into a longer, thinner rod shape can more than double the penetration depth compared to simpler configurations.
What makes EFPs particularly dangerous is that they concentrate all that energy on a single spot. A standard roadside bomb sends fragmentation and blast energy outward in 360 degrees. An EFP focuses its power on one point, delivering far more damage to whatever it hits. Fragmentation still radiates outward, but the primary killing mechanism is that single high-velocity slug. Something weighing just a few pounds, traveling at those speeds, carries enough energy to disable or destroy heavily armored vehicles.
Military Weapons Using EFP Technology
EFP technology appears in several formal military systems. Top-attack anti-tank munitions, designed to strike vehicles from above where armor is thinnest, often use EFP warheads. These can be delivered by missiles, artillery-deployed smart munitions, or increasingly by small drones. The technology is lightweight enough that even small unmanned aircraft can carry an EFP warhead capable of damaging armored targets, a reality that has reshaped modern battlefield calculations. If the software guiding an autonomous agricultural drone can point a camera, it can theoretically aim an EFP, a concern that defense analysts have flagged as a growing asymmetric threat.
Improvised EFPs in Combat Zones
EFPs gained widespread public attention during the Iraq War, where they were used as roadside bombs against coalition and Iraqi forces. The improvised versions followed the same basic physics as military designs but were built from readily available materials. A typical improvised EFP consisted of a copper or steel plate or bowl backed with several pounds of explosives, housed in round pipe similar to irrigation tubing. The cylindrical body included a base plate made from combinations of metal, wood, plastic, and tape.
These devices were often disguised with expanding foam or hidden in piles of roadside trash to break up their outline. They were detonated remotely as vehicles passed. In one operational area in Iraq, 16 EFP strikes were recorded in a single period starting in June 2008, each one posing a serious threat to armored and unarmored vehicles alike. While specially armored military vehicles and electronic countermeasures saved many lives, civilian vehicles on the same roads had no such protection. Innocent Iraqis traveling ordinary roads bore a disproportionate share of the casualties.
Defending Against EFPs
Countering EFPs is harder than stopping conventional roadside bombs. Standard armor designed to resist blast waves and fragmentation often isn’t enough against a focused, high-velocity metal slug. The response has involved several approaches.
Passive armor systems use hybrid modules combining multiple materials designed to absorb kinetic energy, resist mechanical deformation, and dissipate blast energy in layers. One Israeli-designed system provides protection equivalent to 45 to 60 millimeters of standard steel armor while weighing half as much as a comparable solid steel plate. These composite armors can stop multiple hits from small and medium-caliber projectiles as well as EFP slugs.
Active protection systems take a different approach, using sensors and interceptors to detect and destroy incoming threats before they reach the vehicle. Several defense contractors have developed and deployed both passive and active solutions specifically targeting the EFP threat, and these systems became standard additions to armored vehicles operating in Iraq and Afghanistan through programs like the Mine Resistant Ambush Protected vehicle initiative.