Protecting against blast
Briefly (and simplistically) when the threat is a large blast, the vehicle designer should seek to:
- create a stand-off distance between the threat and the vehicle (usually by fitting large wheels)
- break any shock transfer with frangible parts (stub axles may break away, for example);
- deflect blast from the vital parts (usually the passenger area) with thick steel armour plates;
- design a passenger cockpit that is rigid and strong using armoured steel or thick mild steel (depending on required performance and repair facilities, as well as the anticipated threat);
- prevent blast entering the passenger cockpit by avoiding holes facing down (for foot-pedals, etc);
- provide passengers with rigid seating and fixed cross-over belts to hold them firmly down in the seats;
- fit armoured glass to all windows (which are usually reduced in size);
- design so that fuel, battery acid and other fluids cannot enter the passenger area if the vehicle is inverted;
- provide an escape hatch for use if the doors are rendered inoperative (the hatch is often in the roof);
- fit fire-blankets and extinguishers as standard.
The most successful examples of this involve putting the driver and passengers inside an armoured box. Large wheels (sometimes whole axles) are frangible and the box is high enough from the ground to use upward-facing exit-holes for control linkages to avoid trapping blast. The driver and passenger seats should be both rigid and high-backed so that a passenger is strapped down and back into an unyielding seat.
MPVs designed for use in conflict areas sometimes have frangible parts designed to facilitate rapid repair and a driven exit from the threat area. The Wolf (frangible wheels, below) and the Casspir (frangible axles, above) are examples. Users should be aware that rapid replacement requires practice and cannot be done by the driver alone!
Protecting against fragmentation
It is much simpler to protect against simple fragmentation than against a large blast – but fragmentation may not be simple.
Fragments may be:
- shattered parts of an explosive/device that may be superheated and may be parts of a fragmentation case designed to cause penetration;
- shattered parts of the environment formerly surrounding the device (the ground, rocks, etc – which may also be superheated);
- parts of objects between the seat of initiation and you – things that the explosive event has already shattered (glass in a vehicle window, for example;
- scattered secondary or deflected fragmentation or ammunition aimed at another target;
- directly fired ammunition.
The only one of these that can be reliably reproduced in tests to allow a design’s performance to be verified before deployment is “directly fired ammunition”. Generally, because the position of the fragment source cannot be predicted, designing for deflection is limited to the acute angle beneath the vehicle where directly fired ammunition is not a threat, but hidden devices such as mines are. This means that vital parts are usually protected against fragmentation from any angle. This is usually achieved by protecting the cockpit (and sometimes the engine) with rigidly fixed plates of steel armour and armoured glass.
When the threat is small (conventional fragmentation mines at more than 5 metres) aramid and polycarbonate products may be used. When the threat is entirely mine related (and not the deliberately targeted detonation of a device in conflict) the armour can be selectively placed – for example, it may not extend onto the roof.
When the threat will only exist fro short and predictable periods, armoured glass may be sparingly used with other windows covered by armoured shutters.
Protecting against large devices with polycarbonate instead of glass is tempting, especially when the machine operator wants large viewing areas, so large windows. Large panels of thin polycarbonate provide no realistic protection against a large device because they will readily distort and blow out of place, fracture or even tear.
This optimistic roller systems was made for "verification" in Angola. The carrier has good polycarbonate visibility but is not appropriately armoured above, but the same machine is below.
Protecting against shaped charges
Some anti-tank mines include a shaped-charge designed to penetrate the floor of armoured vehicles. Many other munitions (BLU-97 and KB-1 submunitions, RPG7s, etc) include a shaped charge intended to penetrate the sides and top of armoured vehicles. These may be present as UXO and can be an armour-piercing threat when driven over.
Despite its small size, this is what a BLU-97 can do to a thick steel girder.
Mines with a shaped charge are intended to detonate directly beneath the personnel inside an armoured vehicle (tank, etc). To achieve this, they are fuzed with an antennae that the belly of the vehicle bends as it passes. The explosive detonates, turning the shaped charge into an armour penetrating “plasma bolt”. After it has penetrated the armour, it breaks up and bounces around inside the vehicle as tiny pieces of white-hot, high-speed metal.
Stopping a shaped charge reliably requires layers of armour, reactive armour, or – as pioneered in South Africa – a water tank inside the V-hull of the vehicle. Water is heavy, but it apparently works. Generally, the weight and cost involved means that MPVs used in Humanitarian Demining are NOT protected against a shaped-charge threat.
Next: the survivability of materials