Armor Corner: Tank Talk

In this installment of Armor Corner, we’re going to talk tanks, and let other AFVs alone for the time being. We’ll start by discussing some important facts about these armored beasties. First of all, a tank is an offensive weapon. As such, it is not uniformly protected. A tank’s thickest armor is always on the front of the vehicle, facing the enemy. The sides of a tank’s turret and hull are the next most heavily armored. Its rear end is its most vulnerable spot. During WWII many German tanks were so heavily armored that the more lightly armored and armed U.S. tanks could only kill them from the rear. The two most thickly armored parts of a tank are the glacis plate, the upper nose of its hull, and the mantlet, the plate which shields the gun mounting at the front of the turret. One of the greatest innovations in tank designs during the Second World War was sloped armor. When armor is sloped to the angle of attack rather than being perpendicular to it (i.e., vertical), it protects much better for any given thickness of armor plate.

A tank’s gun uses direct fire to do its destruction, hurling a projectile straight at its targets at great velocity. The howitzer of a self-propelled artillery vehicle, on the other hand, lobs shells at its targets indirectly; its targets may, in fact, be miles away. In WWII most anti-tank projectiles were solid shot. They did their damage by penetrating a vehicle’s armor and then bouncing around inside it. Later in that war and after, high explosive anti-tank rounds were developed which literally melt a hole in armor plate, spraying the interior of a stricken vehicle with molten metal, with devastating results. A good tank gun is able to fire a variety of shells; high explosive for use against enemy infantry or fortifications, anti-tank (solid shot or high explosive), smoke shells, etc.

In general, a tank’s gun is rated by its caliber, the internal diameter of the barrel, measured in millimeters. Thus, a 75mm shell is 75 millimeters thick, not long. Another important factor in rating a tank’s gun is barrel length. For instance, reference to a 50mm L60 gun means a gun with a 50mm diameter and a length of 60 x 50mm, or 3 meters. Given the same caliber, a gun with a longer tube will throw a shell with a greater velocity, and velocity is the name of the game.

But a tank’s cannon is not its only weapon. All tanks have a coaxial machine gun, mounted next to the main gun in the turret front. One of this weapon’s main uses, since it is lined up exactly with the larger weapon, is ranging – firing tracer rounds at a target to see if the main gun is on line for a hit. In the “good old days” of WWII, tanks were also equipped with a hull machine gun, located in the front of the vehicle’s chassis next to the driver’s position. In those days a five-man crew was pretty much standard – commander, gunner, loader, hull machine gunner/radio operator, and driver. Tanks these days have dispensed with the hull machine gun, and use a four-man crew == three men if the vehicle has an automatic loader for the main gun. As in WWII, though, today’s tanks usually have machine guns mounted atop the turret for anti-personnel or anti-aircraft use. Another common tank weapon is a launcher for small anti-personnel charges. Such a weapon is used to get pesky (and dangerous) enemy infantry off a tank’s back, much like a high-explosive fly swatter.

So far, we have discussed two of the “big three” of tank design and function – protection and firepower. The third element is mobility. It has often and truly been said that a good tank design is a compromise of these three elements. A tank should have as much protection as possible, if for no other reason than maximizing crew morale, but if a tank’s armor is made too thick, it will be so heavy and so slow as to be practically useless. A sluggish armored behemoth will be outflanked and destroyed in a fast-moving mobile war. The same applies to firepower. Tank firepower has escalated tremendously since WWII, going from a caliber of 20mm to a current average of 120mm for main guns. If designers try to mount too large a weapon in a tank, however, it has the same effect as too much armor – a larger, weightier, and hence a slower vehicle.

Today’s main battle tanks (MBTs) are about as heavy as the most thickly armored vehicles to see service with the German army in WWII, but they are much more mobile and mechanically reliable than those earlier armored giants, thanks to such innovations as the powerful turbine engine mounted in America’s M-1 MBT. The M-1 is capable of a top speed of 55 mph – amazing for a 60-plus ton vehicle. Its speed is governed down to 40 mph, though, for the simple reason that the treads and other suspension components don’t stand up well to high-speed maneuvers.

There you have the most important facts about tanks, ancient and modern. Tank design has evolved a great deal over the years, but one thing that has not changed is the role of the tank in warfare. We’ll discuss that next time.