An EFP, or explosively formed penetrator, is a type of weapon that uses a shaped explosive charge to transform a metal disc into a high-speed projectile capable of punching through armor. Unlike a bullet fired from a gun, the projectile doesn’t exist until the moment of detonation. The explosion itself creates the projectile, reshaping a concave metal plate into a dense slug traveling between 1,700 and 3,000 meters per second.
How an EFP Works
The basic design is surprisingly simple. A metal tube is capped on one end with a shallow, dish-shaped metal liner, usually made of copper or tantalum. The space behind the liner is packed with explosive. When the explosive detonates, the blast wave hits the concave liner and forces it to collapse inward, folding the metal upon itself. In about 15 microseconds, that thin disc has been squeezed and launched forward as a compact, aerodynamic slug several centimeters in diameter and several centimeters long.
This process is based on what physicists call the Misznay-Schardin effect: the observation that an explosive blast pushes outward most forcefully from the flat face of a charge. The effect was named after Hungarian officer Jozsef Misznay and German physicist Hubert Schardin, who studied it during and after World War II, though the underlying science was described as early as 1936.
How EFPs Differ From Shaped Charges
EFPs are often confused with traditional shaped charges because both use explosive force to defeat armor, but they work quite differently. A conventional shaped charge has a cone-shaped metal liner. When it detonates, the cone collapses into an extremely thin, fast jet of molten metal that can travel up to 10,000 meters per second. That jet is devastating at close range but breaks apart quickly, so the warhead needs to detonate at a precise, short distance from the target.
An EFP takes the opposite approach. Instead of a thin jet, it produces a solid, heavy slug that holds its shape as it flies. The slug moves slower than a shaped charge jet, typically 2,000 to 3,000 meters per second, but it stays intact over much greater distances. This means an EFP can be effective from tens of meters away rather than needing to detonate right next to its target. In testing, EFP projectiles have shown displacement of less than 20 centimeters at 45 meters, meaning they fly with remarkable accuracy.
Why the Slug Shape Matters
Not all EFPs produce the same projectile. The final shape of the slug depends on the geometry of the metal liner and how the detonation wave travels through the explosive. A simple design might produce a roughly spherical slug with poor aerodynamics that loses energy quickly in flight. More advanced designs manipulate the detonation wave to produce a long, rod-shaped projectile with a higher length-to-diameter ratio. These elongated slugs cut through the air more efficiently and hit harder at longer range.
Some designs use two layers of different explosives to control the shape of the detonation wave more precisely. Because the two explosives detonate at different speeds, the resulting wave can be tuned to stretch the slug into a longer rod with better flight characteristics. Engineers have also experimented with wave shapers, small inserts inside the charge that redirect the blast for a more uniform push on the liner. The goal is always the same: produce a projectile that flies straight and arrives at the target with as much energy as possible.
Military Applications
EFPs are used across a range of military weapons, from roadside devices to sophisticated guided munitions. Their ability to strike from a distance makes them especially useful in “sensor fuzed” weapons, a category of smart munition designed to find and hit armored vehicles automatically. These munitions are released over a battlefield, descend by parachute, and use onboard sensors to detect vehicles below. When a target is identified, the weapon fires its EFP warhead from several meters or even tens of meters above, striking the top of the vehicle where armor is thinnest.
The U.S. military’s SADARM (Sense and Destroy Armor) program and the CBU-97 Sensor Fuzed Weapon both use this concept. A single artillery shell or cluster bomb can release multiple submunitions, each carrying its own EFP warhead and sensor package. Because each submunition independently searches for a target, a single weapon can engage multiple vehicles across a wide area.
What Makes EFPs Effective Against Armor
The penetrating power of an EFP comes from the combination of the slug’s mass, speed, and cohesion. A shaped charge jet is faster but extremely thin, so it bores a narrow hole. An EFP slug is heavier and wider, so it punches a larger hole and sends more material through the other side. The slug doesn’t melt through armor the way a shaped charge jet does. Instead, it defeats the plate through sheer kinetic energy, like a very fast, very dense punch.
Penetration capability scales with the diameter of the charge. A larger EFP produces a heavier slug with more energy. The material of the liner also plays a role: copper is the most common choice because it is dense, ductile, and deforms predictably under explosive pressure. Tantalum is denser and can produce even more effective slugs but is significantly more expensive.
Because the slug holds together over distance, EFPs are harder to defend against with reactive armor, the type of add-on armor panels that detonate outward to disrupt an incoming shaped charge jet. A solid EFP slug is far more resistant to being deflected or broken apart by such countermeasures, which is one reason the technology has remained a focus of weapons development for decades.