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Military weapons are designed to fulfil a limited function; essentially, they are directed towards a target upon which they are expected to inflict the maximum amount of damage possible. It can sometimes seem that this is a fairly simple task, but in practice there have been many developments to ensure the effectiveness of weapons against their most likely targets.
Essentially there are three problems that every major weapons system has to face:
- How to get to the target
- How to destroy the target
- How to do all this without becoming unwieldy
You could, for example, destroy a tank by dropping a five hundred tonne mass on top of it. It would be a simple and effective solution - cheap too. Unfortunately, you then have to devise a machine capable of carrying such a mass and dropping it accurately. Accordingly this is not a preferred method for attacking armoured vehicles.
Explosives are used throughout military technology. They launch ejector seats out of damaged aircraft, propel rockets towards their targets, ignite to spread chaff to deceive RADAR, launch decoy flares to distract infra-red homing missiles, and drive bullets and shells through gun barrels. They are also a 'force multiplier'; they can be packed into a ten kilogram shell and make it as lethal as dropping a ten tonne weight. When first introduced into shells in the 19th Century, they consisted of a simple filler of explosive packed into a steel casing. Since then there have been special warheads designed for almost every type of target imaginable.
For use against personnel and unarmoured targets, the preferred type of warhead is fragmentation. The earliest types of explosive shell were effectively fragmentation devices which split into large pieces of jagged metal when the shell detonated. During the Second World War, large numbers of hand grenades were produced with a 'scored' pattern impressed into the steel casing to aid fragmentation. In practice this proved ineffectual, as the casing didn't break along those fracture lines.
Such grenades are very dangerous for the user as well as the target; when accelerated by the force of the explosion, large pieces of casing are thrown great distances. Modern fragmentation grenades tend to be plastic-cased with a ball of fine wire wrapped around the explosive core to provide fragmentation damage. In such devices the wire is too light to retain its speed over distance, in these grenades, therefore, there is a relatively 'safe' point at a measurable distance. Obviously the wire does not penetrate personnel targets as effectively as larger metal fragments but the sheer quantity of fragments produced causes a vast number of painful and incapacitating injuries and these can prove particularly difficult for medical personnel to treat.
In larger weapons, fragmentation shells are often used as preparatory barrage for an infantry assault. Deployed over soldiers in trenches and other improvised shelters they are fused to explode above ground. Such weapons are also used to break up infantry attacks, clear minefields and to destroy wires and cables, especially where used to prepare a valuable target for demolition by explosive.
Armoured vehicles are designed to protect their occupants and their operation from damage. In order to qualify as armoured, a vehicle or ship should, at least, provide protection from fragments and infantry bullets. Up to a certain armour thickness, it is possible simply to increase the mass or velocity or both of a bullet and still effect penetration. Heavy machine guns and anti-tank rifles have been variously used for this purpose.
After that point the armour becomes so thick that it is unfeasible to break through by using a simple, man-portable device such as a rifle. Once again, explosives are used to raise the stakes.
When originally introduced onto ships, armour simply consisted of steel plates, however there are four significant improvements to armour which many modern vehicles have employed:
Steel shatters if it is hardened too much, so armour is usually made of relatively ductile (soft) metal. This permits designers of armour piercing weapons to design them hardened knowing that they will hit a relatively yielding surface. Designers of armour have developed the ability to harden only the outer face of an armoured plate, with the potential of shattering the incoming projectile while not compromising the overall ductility of the armour.
Over the top of armoured plating there can be a second armour surface with a space between the two. The projectile can be deflected by the first plate into a less harmful trajectory1 or the fuse can be initiated by the outer plate before the projectile has reached the main armour.
If a projectile strikes armour at a sharp angle then it has a greater chance of bouncing off. The greater the actual depth of armour plate to penetrate, the more likely it is that any blast effects are deflected away from the area behind the armour. With these benefits, designers usually slope armour wherever possible.
Many modern tanks are protected with a composite armour developed in Britain and called Chobham. Which consists of layers of steel separated with ceramic plates. Some US warships use DuPont Kevlar as lightweight armour for the superstructure.
'High Explosive Squash Head' projectiles have a softened ogive2 that flattens against armoured targets. When detonated, the explosive delivers a powerful shock-wave through the armour - enough to shatter the inside surface into high-velocity fragments. In most cases the armour is not actually pierced, but fragmentation damage inside can be severe.
HESH warheads are ineffective against spaced or composite armour, have massively reduced effectiveness against steeply sloped armour and are vulnerable to damage if striking face-hardened armour. HESH warheads are no longer seriously considered as armour-piercing weapons since newer forms of armour have rendered the technology obsolete. HESH warheads are still in use in second-line functions because the explosive content of the warhead can produce more damage in unarmoured vehicles than an APDS type which will essentially punch through without slowing down, not imparting much of its energy into the target.
'High Explosive Armour-Piercing' projectiles consist of a thick-walled hardened steel case with a fuse on the base operating on a time delay. They are fired at high velocity and are designed to smash a hole through armour and detonate on the other side. They are vulnerable to shattering against face hardened armour plate, and are much less effective against highly sloped armour, but are relatively unaffected by spaced plates and composite armour.
'Armour-Piercing Cap' projectiles are HEAP projectiles with a rounded (blunt) soft cap placed over the sharp armour-piercing ogive. The soft cap deforms on impact providing a ductile outer surface for the HEAP warhead to drive through. This vastly reduces the extent to which both sloping and face-hardening affect the projectile.
'Armour-Piercing Cap Ballistic Cap' projectiles are APC projectiles with a lightweight streamlined cap over the armour-piercing cap. This has no effect on the armour penetration of the projectile, as it shatters on impact, but does permit a more aerodynamic shape than an APC shell, thus reducing drag and increasing impact speed.
'High Explosive Anti-Tank' warheads use a shaped charge detonated a known distance from the armoured surface. The shape is concave on the front face of the warhead. When detonated, the shape of the explosive forces a 'jet' of superheated gas forward in a tightly narrow beam into the armour. Due to its high temperature and huge velocity this gas jet blasts a narrow hole through armour. HEAT warheads are used in most infantry anti-tank weapons because the effectiveness of the warhead is not dependent on the speed with which it strikes the target. It is therefore suitable for rocket launchers, low-velocity guns and recoilless-rifles.
HEAT projectiles are effective irrespective of face-hardening and suffer relatively little due to armour sloping, they are quite impeded by spacing of armour and rendered almost ineffective by composite plates.
'Self-forming Fragment' projectiles are similar to HEAT warheads except that the concave surface of the explosive has a thin layer of metal placed over it. When the explosive detonates, the metal is forged into a streamlined fragment and accelerated towards the target. SFF warheads are less effective than HEAT warheads but have the advantage that they do not need to be a known distance from the armour plate when detonated.
They can be used mainly to attack relatively poorly protected areas of armoured vehicles such as the grilles above the engines. SFF projectiles are significantly affected by sloped armour and spacing, and somewhat less affected by face-hardening and composite armour.
'Armour-Piercing Discarding Sabot' projectiles are used by most modern high-velocity tank guns for attacking other armoured targets. They do not use an explosive warhead but instead use a narrow 'dart' made of a dense and hard substance such as tungsten or depleted uranium3. The dart is of a much smaller calibre than the gun that fires it, so it is surrounded by a 'holder' or 'sabot'4 of the calibre of the barrel. Once the projectile is in free flight the sabot falls away leaving the dart to strike the target. APDS projectiles are only effective in very high-velocity weapons but because of their speed they are relatively immune to any cunning on the part of the armour designer. Their speed also reduces the time between firing and impact and therefore makes APDS warheads very accurate. Generally APDS projectiles are either spin-stabilised (APSSDS) or fin-stabilised (APFSDS).
Other Types of Warhead
HE warheads are hollow casings containing explosive. They do the majority of their damage by the shockwave caused when the explosive detonates. They can be considered as fragmentation warheads without any additional components added to provide fragments, are used with impact or delayed-action fuses and are frequently used in aircraft bombs for destroying buildings and other unarmoured structures.
FAE warheads use a tank of fuel (gasoline, kerosene, etc) which is distributed by the impact of the bomb into an aerosol, which is then detonated causing a huge explosion. The shockwave of an FAE bomb is second only to that of a nuclear device and they can be used to clear minefields, destroy buildings and obliterate 'soft targets'.
WP warheads contain a chemical compound of phosphorous that burns at a very high temperature. The reaction is ignited by a detonator in the shell casing and the effect is to produce a bright burning impact mark and a vast amount of thick smoke. Initially the use of the shell was purely for chemical smoke, however subsequent adoption of this rather expensive compound is closely related to its secondary function as an anti-personnel weapon.
WP burns at a very high temperature and is extremely difficult to quench, it is also 'sticky' meaning that the burning chemical has a tendency to be difficult to remove from people it comes into contact with. Horrific injuries are frequently caused by WP ammunition, and since the 1960s, WP compounds have been added to the explosive fillers of some air-dropped bombs for attacking personnel targets.
Napalm is simply a production-line automated version of the 'Molotov Cocktail'5 and consists of a jellified liquid fuel and a fuse to ignite it. On impact the outer bomb casing splits and the burning fuel is spread over a wide area. Only the United States has ever issued napalm bombs to their forces and the use of the weapon has so far been limited to operations in South-East Asia during the 1965-75 Vietnam War.
Starshell, or artillery flares, are generally a highly complex multipart system. Designs vary, but the shell has a timed or altitude fused explosive charge which detonates to break the outer casing of the weapon, within which there is a parachute or similar device to slow the descent, and a chemical flare (often magnesium metal) which burns brightly enough to provide useful illumination over a target at night.
Starshell is used in all forms of warfare, but historically has been most common at sea; warships have used starshell from the secondary weapons to illuminate a target for the more powerful primary weapons. With the advent of modern RADAR and fire-control, the use of the weapon has declined at sea. Naval starshell was often simpler than that used on land, lacking the parachute and relying on a high rate of fire from multiple barrels to provide continuous illumination.
Essentially a hollow canister containing either pressurised gas or, more commonly, a liquid spread as an aerosol. Chemical weapons are regulated by international agreements and cover the range of substances from blister agents like chlorine gas to nerve agents like Sarin and VX.
Similar to chemical devices, these are hollow casings which split violently when subjected to a high-speed impact. Biological weapons are usually liquid-based, often a saline solution with the active particles suspended within. Biological weapons distribute disease-causing particles on detonation, influenza and Anthrax being the most popular choices. Like chemical warheads, these are also governed by international treaties.
All forms of fission and fusion based explosion are defined as nuclear weapons. Nuclear warheads appear in several different forms.
A reaction mass of uranium (uranium 235) or plutonium is initiated by conventional explosives, supplying sufficient pressure and temerature to cause a fission chain reaction to initiate. The reaction causes the production of neutrons in quantity, some of which strike other metal atoms producing more neutrons. The result is an extremely energetic reaction. Atomic bombs have twice been used operationally by the United States against Japan at the end of the Second World War; they are the only type of nuclear warhead ever to have been deployed.
Hydrogen bombs, or two-stage devices, use the energy from an atomic bomb to initiate a fusion reaction in a 'hydrogen' source. The hydrogen is a mixture of radioactive tritium and deuterium gas, and the energy released by a fusion reaction is orders of magnitude greater than can be achieved by a single-stage atomic bomb.
A hydrogen bomb has sufficient energy that it can be used as the initiator for a third stage, usually causing the fission of a surrounding casing of uranium 238 (sometimes called a neutron bomb). There are additional stages that can be applied beyond this but they simply raise the eventual yield.
Nuclear explosions are measured in terms of megatonnes (or kilotonnes), which is the explosive power of a million tonnes (or a thousand) of TNT (Trinitrotoluene), a standard conventional explosive. The atomic devices dropped on Japan in 1945 by the USA were of the order of a few tens of kilotons. The USSR once tested a hydrogen bomb with a power close to 100 megatons.