An Exhaustive Classification of Ammunition

A projectile can be fully classified along three distinct axes: its overarching purpose, its physical effect on the target, and its method of actuation.

Axis 1: Intended Purpose

The highest-level classification is the reason the round exists. There are four main purposes. The first is destructive or lethal, the goal of which is to destroy equipment or kill personnel. This category includes the vast majority of military ammunition. The second is support or utility. These rounds are not designed to destroy but to alter the battlefield, such as smoke rounds for concealment or illumination rounds for visibility. The third purpose is training. These rounds are either completely inert drill rounds for handling practice or target practice rounds that match the ballistics of a live projectile without the explosive filler. The final category is less-lethal, designed to incapacitate personnel or vehicles without causing permanent destruction, such as rubber bullets or tear gas canisters.

Axis 2: Terminal Effect

This axis describes the physical principle the projectile uses to achieve its effect at the target. These principles fall into two main families.

Kinetic energy projectiles function as a hyper-velocity hammer. A full-bore penetrator, like an armor-piercing (AP) round, is a solid slug of hardened material that punches through a target with its own mass and momentum. A more advanced sub-caliber penetrator, like an Armor-Piercing Fin-Stabilized Discarding Sabot (APFSDS), uses a lightweight sleeve, or sabot, to accelerate a smaller, denser dart to extreme velocities. The sabot falls away after leaving the barrel, allowing the dart to fly to the target.

Chemical energy projectiles use a reaction to create their effect. A High-Explosive (HE) round detonates to create a blast wave and shrapnel. A High-Explosive Anti-Tank (HEAT) round uses the shaped charge principle. A conical liner inside the explosive is collapsed into a hypersonic jet of superplastic metal that drills through armor. The High-Explosive Squash Head (HESH) round uses a spalling effect. Its malleable explosive charge flattens against a target before detonating, creating a powerful shockwave that breaks off a lethal piece of armor from the interior face.

Axis 3: Actuation and Delivery

This axis defines how the projectile functions. Guidance describes its flight path. Most ammunition is unguided, following a simple ballistic arc. Guided munitions can alter their course using systems like lasers or GPS. Fuzing is the projectile’s brain. A point-detonating fuze functions on impact. A delay fuze functions a fraction of a second after impact. A proximity fuze uses sensors to detonate at a specific height above the ground.

The Intractable Problem of HESH

The HESH round poses a fundamental challenge to armor design because its kill mechanism bypasses conventional penetration physics. Its counters are few, and each possesses critical, unresolvable flaws. The HESH principle is an attack on the integrity of the target material itself. A shockwave is a holistic event that exploits the material’s inevitable microscopic imperfections. It finds and widens these flaws, causing a brittle failure from internal stress.

One defense against this is spaced armor, a thin outer plate separated from the main hull by an air gap. This system functions by triggering the HESH detonation prematurely. The shockwave is created on the outer plate and cannot effectively cross the air gap to the main hull. The flaw in this design is its endurance. The thin plate is not merely sacrificial; it is a single-use component. A HESH detonation will cause a catastrophic failure of this plate, shattering it and potentially tearing it from its mountings over a wide area. It is a system designed to fail completely in order to work once.

Another defense is composite armor. This system relies on heterogeneity, a “dumb complexity” of layered materials like steel, ceramics, and polymers. It does not possess a sophisticated synergy. It functions as a mechanical filter. Each interface between materials of different acoustic impedance reflects and scatters the shockwave’s energy. This is a process of attrition against the wave itself. The system’s weakness is cumulative damage. Each impact, even if not fatal, shatters the internal ceramic layers and degrades the bonds between materials. The armor’s integrity is a finite resource that is consumed with every hit.

Theoretical defenses like electric armor are also mismatched to the threat. Such systems use a powerful electrical discharge to vaporize or electromagnetically propel a projectile. While the system’s electrical power is great, its physical structure of thin capacitor plates is weak. A direct HESH detonation on the armor’s surface would physically obliterate the electric armor module, creating a massive breach. More fundamentally, these systems act on the projectile before impact. They do nothing to counter the shockwave itself once it has been generated and is propagating through the main hull.

The Challenge of the Tandem-Charge HEAT Warhead

The HEAT warhead, with its focused metal jet, has also driven a intense cycle of defense and counter-defense. While effective systems have been developed to defeat single-charge HEAT warheads, the offense has evolved in response.

Armor systems provide effective protection against standard HEAT rounds. Explosive Reactive Armor (ERA) uses an explosive-filled brick to propel metal plates into the path of the jet, shearing it apart. Non-Explosive Reactive Armor (NERA) uses a bulging motion to disrupt the jet’s path. These systems are effective at what they do. They successfully counter the threat they were designed to face, forcing offensive weapon designers to find a new solution.

The solution was the tandem-charge warhead. This weapon is a specialized tool designed to defeat layered defenses. It consists of two shaped charges aligned in a row. The first, a small precursor charge, has one job: to defeat the outer defensive layer. It expends its energy detonating the ERA brick or punching through the initial plate of a NERA or spaced array. The individual ERA brick is a single-use component. Once it detonates, it is gone, leaving a localized point of vulnerability.

The main charge detonates a microsecond after the precursor has cleared the path. Its powerful jet travels through the channel created and strikes the main armor plate, which was previously protected. The tandem charge’s effectiveness comes from its ability to sequentially neutralize a multi-layered defense. It is a purpose-built key for a complex lock, demonstrating the persistent, cyclical nature of the contest between armor and anti-armor munitions.

Conclusion

A first-principles approach to ammunition reveals the core physics behind its design and effectiveness. Kinetic rounds use force, while chemical rounds use reactions. The defenses against them must address these specific principles. This analysis demonstrates that the HESH round remains a uniquely challenging threat. Its kill mechanism attacks the fundamental integrity of materials, and its counters are either single-use, finite in their endurance, or physically mismatched to the problem. The HEAT warhead spurred its own set of effective defenses, but these in turn were met by the evolution of the tandem charge. This perpetual race between offense and defense shows that in the world of armament, there are no absolute solutions. There are only temporary advantages in an ongoing struggle governed by the laws of physics.