36 · MT 3/2022 Feature 1.5m of rolled homogeneous armour (RHA), for instance. However, the small diameter of the jet can limit lethality, requiring more rounds to achieve target defeat when compared with APFSDS. The IDF example above demonstrate this; it is unlikely that a similar number of successful APFSDS penetrations would have resulted in such low casualties. Medium Calibre Medium calibre cannons are near ubiquitous, ranging from the 23mm GsH Shipunov 23x152mm, through the quintessential M242 Bushmaster, chambered in 25x137 mm, to cased telescoped 40x255 CT40. The increase in calibre allows for introduction of either armour-piercing discarding sabot (APDS) or APFSDS rounds, representing some of the most potent threats a light or medium AFV might face. Medium calibre threats use the armour defeat mechanisms described above for large calibre munitions, but in miniature, Keçeli explained. However, there is one important consideration that does not typically apply to large calibre effectors – rate of fire. Consider the Soviet 57×38mm S-60 air defence cannon with a sustained 70rpm rate of fire. The kinetic energy of its HE projectile is sufficient to penetrate a T-55’s turret sidearmour. A 30mm cannon, such as the Shipunov 2A42, can also deal considerable damage to a tank, shredding tracks, igniting fuel and damaging sights, as video footage from Ukraine shows. Rate of fire is therefore an important element in achieving behind-armour effects – a single 30mm round may not be sufficient to defeat a medium AFV and its crew, but the weapon’s value and lethality rests in the four or five rounds that follow in quick succession, multiplying those effects. Equally, the role of fragmentation in medium calibre munitions must be considered. It is a threat not applicable to heavy machineguns and can include specialised munitions, such as proximity-fuzed rounds for enhanced lethality. “Specialised ball bearings inside the wall of a munition widens the tactical range at which these rounds can be used,” Keçeli explained. “Hardened ball bearings have great flight characteristics, can travel far beyond any chaotically-formed shrapnel, and can induce higher damage due to their stable impact geometry”. While their effects will be limited against AFVs, they could be devastating against unarmoured which, with tungsten and DU rounds, can atomise both armour and penetrator. “When the armour fails, all those super-heated particles fill the interior of the vehicle and mix with the oxygen, creating perfect conditions for an oxidation reaction which is highly exothermic. The combustion of these already energy-intense particles turns the inside of the vehicle into an oven,” Keçeli said. This blast and superheated projectile fragments also pose significant risk to sowed ammunition, resulting in a catastrophic detonation. Keçeli also invokes consideration of a Newton’s Cradle effect: the projectile propagates shockwaves through the armour, so nuts, bolts, and broken armour can create additional shrapnel effects. This is possible even when the projectile does not pass through the armour. HEAT – So Hot Right Now High explosive anti-tank (HEAT) munitions use explosively-generated chemical energy to form a penetrator. The explosive is shaped around a hollow material – typically a ductile but tough metal like copper, with an apex point, often - though not always – cone-shaped. Detonation collapses the cone and focuses it into a single point. The tip of the cone accelerates away from the base, reaching speeds of around 6-10km/s, which can vary throughout the length of the jet. The jet is, in fact, a solid, but the forces it is subjected to mean it is characterised by the laws of hydrodynamics. The principles defining a HEAT jet are essentially the same as for an APFSDS round; it penetrates the armour with kinetic energy, rather than melting it, which is a common misconception. However, the penetrator is very thin and so creates a smaller hole. Nonetheless, once through the armour, it generates similar behind-armour effects to a long rod penetrator, including spalling and jet fragmentation. Other effects peculiar to HEAT penetrators include overpressure created by detonation, which can send shockwaves through the vehicle, impacting soft tissue. A further element is the liner material: aluminium liners, for instance, can oxidise and ignite diesel. The energy and heat of the jet itself can also be sufficient to detonate stowed ammunition. HEAT projectiles are typically capable of penetrating more steel than an APFSDS. Some modern designs are credited with the ability to penetrate Modern cannons have a variety of munitions available to them. The CT40 has an extensive suite of munitions including an APFSDS, point detonating and airburst natures. (Photo: Reise Reise, CC BY-SA 4.0 via Wikimedia Commons) The M829A2 shown here is an example of an APFSDS round. It demonstrates the length of the projectile and the sabot towards the tip of the penetrator. (Photo: US Army) This image shows the entry hole into an Iraqi T-55 during the first Gulf War. The monolithic steel armour of the T-55 could lead to the effect known as plugging. (Photo: Tech Sgt Joe Colman) e h
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