Tank designers fight new battles

Press, 30 May 1983, Page 16

Tank designers fight new battles

From ‘The Economist,’ London

The heart of the modern European army is the main battle tank. Today on average it weighs about 60 tonnes, carries four men, is driven by a diesel engine of around 1000 horsepower, and fires a projectile on a very flat trajectory over a range of about eight miles. Great debates rage over the virtues of light-agile tanks and the heavy slug-it-out types, of small versus large guns, and of threeman or four-man crews. Inevitably, the question is asked: “Is the tank' really dead now helicopters have so much firepower?” Technological advances are rapidly changing the tank into a substantially different beast from this average one; they may decide all of the arguments. Perhaps the most important advance was the British invention of Chobham armour, a club sandwich of steel and other substances, the exact formula for which has still not leaked into the public domain. It was developed to cope with what was the main threat to tanks, the shaped charge. This charge was invented during the Second World War, but has been much improved since. The explosive is shaped like a cone, with its apex pointing away from the point of the projectile that carries it. When the projectile strikes the taget, the cone-shaped burning surface focuses the energy of the charge at a point, creating very high temperatures that melt through the armour and allow the burning explosive to penetrate into the tank’s interior. One refinement is to line the cone with a layer of copper. The copper melts instantaneously on impact and not only helps with the hole-burning task, but also creates extra havoc inside the tank. Because shaped charges depend on chemical energy instead of raw hitting power for their penetration, they are effective even when propelled by low-velocity rockets that can be carried by infantry or helicopters. Their development thus meant that although the tank was not dead it was in trouble. High-speed armoured thrusts into an enemy’s rear became a risky business; tanks needed infantry, artillery and anti-aircraft protection to keep the shaped charges at bay. Then came Chobham armour. The principle is that the steel outer surface breaks up the shaped charge and the inner layers provide lateral paths of less resistance which dissipate the energy

of the explosive and prevent it from burning directly inwards. The main effect of Chobham armour was to make small shaped charges obsolete. Although huge shaped charges can still do them a mischief, tanks protected by laminated composite armour are safe from most weapons used by infantry and helicopters, and from shaped charges fired by other tanks: The main drawback to Chobham armour is that it is hard to manufacture, form and attach. This is partially offset by the fact that rounded corners are no longer necessary. Since Chobham armour derives its strength from its heatdefeating composition, it does not depend on bouncing projectiles off its surface. So it can be used effectively in big vertical slabs. Another advantage is that it permits a lighter inner structure of the tank. With homogeneous armour the structural framework of the tank forms part of the protection system. With Chobham armour the structural members can be made of aluminium, saving weight. Of the three tanks now using Chobham armour — the British Challenger, the American Abrams, and the West German Leopard 2 — the Challenger has the best protection because it uses the most armour, but the Abrams makes the best use of it by having a lighter framework. Beyond Chobham, or conceivably for use in conjunction with it, is active armour. As shaped charges became less effective,

long-rod penetrators have taken their place as the main anti-tank projectile used by other tanks. These are long darts, an inch or so in diameter and more than a foot long, encased in a steel sabot, or plug, which fits into the gun barrel. After firing, the sabot comes apart and drops clear; the long dart flies on to the target and strikes it with tremendous energy, drilling its way through by brute force. Chobham armour provides a better defence against long-rod penetrators than homogeneous armour, but all armours can be penetrated given the right sort of hitting power. Active armour uses small explosive pads on the outside of the armour to disrupt the flight of the long darts. A number of different arrangements have been tried; one version uses small squares.

When one of the squares is struck by an incoming projectile, the impact fires it; the explosion then causes the dart to yaw, so that its axis is no longer the same as its direction of flight. This either breaks the dart up or sends it skittering away. So far no N.A.T.O. or Warsaw Pact country has put active armour into service. However, American intelligence officials estimate that the Israeli Army deployed it on the Merkava tank during the invasion of Lebanon. The dynamics of active armour are extremely complex, and research still goes on. Although

few scientists are today willing to predict as much, it is possible that ordinary armour with active explosive coverings could supplant Chobham armour as the main tank protection surface within a few years.

The protection of tanks involves more than armour: it also means keeping the target size down. A tank’s costs include manpower as well as its purchase price. An automatic gun loader that could make a big contribution to protection and economy is on the way. It could do away with one crewman per tank and could allow the gun to be mounted outside the armoured box, which could then be made much smaller. Automatic loaders are not exactly new. Sweden had one in its S tank — the “topless” tank — 10 years ago. The Soviet Union has one in its T-72. Both speeded up the rate of fire and allowed three-man crews. Neither, apparently, was considered reliable enough to be put, along with the gun itself, outside the tank’s hull. No N.A.T.O. country has so far put into service an automatic loader. Building a reliable autp-loader is mostly a matter of meticulous design, painstaking mechanical engineering and close-tolerance manufacturing. One reason why N.A.T.O. has never been keen on auto-loaders is that few planners thought cutting

tank crews was a good idea, autoloader or not. Most commanders reckoned that four men was the right number for tanks that might have to go on fighting for days and nights on end. Now, however, with West Germany heading for a military manpower shortage in a few years, the arguments for smaller crews are being revived. Removing the gun from inside the tank may be a bitter pill to some senior officers to swallow: after all, it has always been inside, hasn’t it? But a reliable autoloader makes it possible to put it outside, and the military benefits are considerable. Without having to cover the gun. less armour is needed; some of the saved weight can be used to give better protection to the crew. The silhouette of the hull can be made much lower, and the gun can have a better depression angle.

Big depression angles enable tanks to hide behind the crests of hills and fire over them, but in the past the greater the depression angle that was provided, the higher the turret had to be. Without a turret, the rear of the gun can stick up as high as it needs to. Prediction: no matter what the helicopter advocates say, there will be at least one more generation of N.A.T.O. tanks; they will have automatically loaded guns outside the hull and three-man crews.