Modern light tanks, defined here as weighing less than 20 tons, are valuable in many situations. They are airmobile aboard common mid-sized aircraft like the C-130, and can be amphibious, which allows numerous advantages including water-landing by CL-130 Seaplanes. They can cross bridges too weak for 70-ton heavy tanks and burn one-third the fuel of heavy tanks, which makes a difference in long-range offensive operations. They should be armored to resist small arms fire -- up to 12.7mm heavy machine gun and heavy caliber rifles. It would be nice if their side armor could withstand RPGs and 20-40mm auto-cannon fire, but that is impossible for a light tank.
The problem light tank designers face is the turret and chassis must withstand recoil of the main gun for thousands of firings. In addition, the popular 105mm gun does not have the power to penetrate the frontal armor of a modern heavy tank. Firing a missile rather than a gun projectile eliminates these problems and doesn't require a complex stabilized gun nor a long barrel, although a stabilized target sight is required to fire on the move. Since the recoil of firing a missile is minor, the firing tube can super-elevated to fire missiles upwards at tall buildings, mountainsides, helicopters, or for very long-range engagements. The launch tube does not heat up to produce an infrared signature, and does not have to be replaced every few years. In addition, the short launch tube is much lighter than a gun barrel, and is less restrictive in tight terrain like cities and forests.
This was the basic idea for the M551 Sheridan light tank (right) developed for the US Army in the 1960s. However, its electronics were crude and the tank also fired a large conventional 152mm low-velocity round with poor accuracy. It also fired the Shillelagh missile, but that was one of the first guided munitions with low reliability. An excellent missile system has already been developed and proven for a modern light tank -- the proven laser-designated Hellfire missile.
The $100,000 laser-guided Hellfire is great when pinpoint accuracy is required, or the target is at long-range. However, if this "Helltank" is needed to provide bombardment firepower at prepared enemy positions, it can fire a $2000 dumb rocket, identical in size to the Hellfire, except with more explosive power in place of the sophisticated internal guidance system. This 7-inch (178mm) rocket will have a blast-fragmentation warhead rather a shaped anti-tank warhead. These cheap rockets can also be used by attack helicopters. Hand-loading a 100lb Hellfire missile or rocket is impractical. Some type of autoloader is needed, but the Hellfire only requires two types of munitions, a guided missile or cheap rocket.
Another advantage of Helltanks is the laser-guided Hellfire is a good anti-helicopter weapon, and may shoot down attack aircraft if provided with a long, clean shot. Perhaps an anti-aircraft Hellfire can be developed, with a proximity fuse or an infrared seeker. While a Hellfire may not penetrate the frontal armor of modern heavy tanks, the impact of this supersonic missile will stop a tank cold after causing major damage. Hellfires have far more range than tank guns, although expensive laser-guided tank rounds for long-range indirect fires have been developed. However, tank rounds lose velocity at long range, while a Hellfire missile does not. The Helltank will include the standard .50 caliber machine gun for the commander's hatch, and its coaxial machine will have a .50 caliber as well. This provides much more punch than the common 7.62mm coaxial gun, and more range, which is important since light tanks should avoid close engagements.
Few army officers understand the value of amphibious armored vehicles like Helltanks or the Russian BMP-3 (left) for a tactic like river cruising. An entire brigade may enter a large river at dusk in single file and turn downstream. Only around three feet of the vehicle will extend above the water, while the engine is literally underwater, which shields most of its noise and infrared signature. The current in most rivers is strong enough so that engines can be shut off and the vehicle guided with its steering vanes. This allows a brigade to ride the current downstream at night in total silence with zero infrared signature. Unless an enemy is expecting such a tactic, the brigade should be able to ride the river past enemy lines for almost a hundred miles overnight without burning any fuel. This allows Helltanks with amphibious APCs to bypass defenses and appear far in an enemy's rear area, or by passing through "impassible" mountains and forests by using rivers and lakes as roadways.
This Helltank will be equipped to function as an unbeatable antitank system. It can locate just behind a berm or hillside. The gunner can take his portable laser designator to a good location a few dozen meters from his tank and dig in deeply. From there he can use a radio to tell the tank commander the basic location where to aim the tube to fire Hellfires or rockets just over the top of the thick berm. Laser designating from a hidden location, he can devastate an attacking armored force, including supporting helicopters overhead. Attacking tanks may fire at the source of the missiles, but a thick berm or hillside should protect the light tank, while the gunner continues to designate targets from his foxhole. Another option is to equip a Helltank with a periscope targeting system.
Helltanks will be vulnerable to RPG fire and automatic cannon fire from the flank, but the same is true for APCs. Helltanks will prove superior to heavy tanks in many roles, but assaulting prepared enemy positions is not one of them. Heavy tanks are much better for close combat, but far more expensive, burn three times more fuel, are not easily airlifted, are too dense to float for amphibious crossings, are too heavy for many bridges, and have little defense against attack helicopters. In many situations, especially in wide open country, Helltanks will prove superior with their greater mobility and longer-range weapons system.