I've spent a great deal of time in years past defending Nato from the Russian hoard, and more recently, saving France from the Nazi blitz. Since I'm too lazy to read anyone else's rules, I write my own, achieving just the right blend of playability and realism (well maybe not). Anyway, while writing rules I've spent a lot of time reading propaganda and formulae describing how tank guns work and thought I'd share some of this with our really bored members.

Line of Sight and Trajectory

For modern guns, these are essentially the same thing. One of the best sources for arguments in my games involves a tank shooting at a hull down tank that isn't ... or maybe it is.

Lets talk about the L7 or M68 series 105mm antitank gun for a moment. It armed most of Nato from the 1960's until the mid 1980's in the Leopard 1, M60, M48A5, the early M1, some Centurions, etc. The standard APDS (solid shot) round travels at slightly upwards of a mile per second. As the shot arcs over 1800 yards towards the target, it rises and falls about 12 inches. The Israelis discovered that bore sighting was quite accurate during their conflicts. This meant that instead of ranging the target, they simply opened the breech and looked through the barrel of the gun to aim. Incidentally, the Israelis also found that if they fire three shots at their target, they virtually always got a kill.

This means that if there is a 4 foot tall stone wall between the shooter and shooted, and they are all at the same elevation, that the shooted is essentially hull down, even if the shooted is several hundred yards away from the wall. This may sound nuts, but if the round was in line with the wall, it simply doesn't rise enough to clear the wall in most cases. As the gun gets older (i.e. Korea, WWII), the amount of rise in the arc increases. The main effect is that the range of the gun decreases, but more often than not the round will still hit that wall.

If a HEAT (uses chemicals to burn through the armor) round is fired by the same 105mm gun, it has a better chance of clearing that wall because it travels at a slower speed, but it also takes longer to get there. This means the target has more time to move from where it was when it was shot at, and temperature, wind, and low flying chickens have more time to deviate the round. HEAT rounds are less accurate because of the speed and a bunch of other things that I mention below.

Firing a Tank Gun

From WWII until the late 1970's being a gunner and firing on the move is something like throwing thread through the eye of a needle while riding in a suitcase that is setting on a running jack-hammer.

It's cramped, hot, smelly, smoky (after a couple of rounds), really loud (just from the engine), and extremely bumpy. The profile for the perfect gunner in a T-72 is a 5'-4", 150 pound, left handed individual. Loaders frequently have to stand while the gun is in operation, and in some tanks, such as the T-34 (76.2mm versions) the turret floor (also called the turret basket) doesn't rotate with the turret. That anyone can operate efficiently is quite a statement for the persistence of the human being.

The newer generation of super tanks such as the M1, Challenger, and Leopard II are far superior to the older tanks, but fall far short of riding in a luxury sport sedan.

Even though the crew is trained in the operation of the tank, things can go wrong. The loader can locate the wrong ammo, miss-hear the ammo type being called out by the commander, the round can misfire, the gunner can locate the wrong target, or fail to locate a target, controls can fail, lenses can be damaged, etc. And all this while people are trying to kill you.

Ammunition Types and Gun Design

Since WWII tank guns have advanced a long way. Ammunition types vary greatly, employ several different concepts for penetrating armor and are generally identified by a series of seemingly meaningless letters.

During WWII most tank guns relied on solid shot. The most common were known as APC or APBC. These stand for Armor Piercing Cap and Armor Piecing Ballistic Cap. These are fundamentally the same thing; the penetrator is a large bullet of hard metal that pushes a hole through the armor. These are referred to in the lab as kinetic penetrators, and out of the lab as solid shot.

Another common type of ammo was APHE or Armor Piercing High Explosive, which has a hard metal penetrator and an explosive charge. The idea being that round would punch through the armor, and then an explosive charge would detonate inside of the tank, resulting in dead crewman.

Towards the end of the war something new called APDS Armor Piercing Discarding Sabot was used, most effectively in the British 17pdr gun. The round looks like the front of a skinny dart sticking out of a tube. The penetrator is a long, dart-like object that is usually half to a third of the bore diameter of the gun. A multi-piece light weight sabot is rapped around the penetrator bringing the diameter of the warhead up to the bore diameter of the gun. When the round is fired, the wind resistance on the front of the sabot forces it to brake away or be discarded. The extremely heavy dart like penetrator then hits the target displacing its energy over a small cross sectional area having the diameter of the dart. The advantage is that the penetrator has almost as much force as solid shot, but uses it over a much smaller area. The result is that the APDS round has much better penetration and longer range due to less wind resistance on the small diameter dart during flight.

The penetration of solid shot penetrators is effected by slope of the armor. If a 60mm armor plate is verticle, the round has to penetrate 60mm. If the 60mm plate is at 30 degrees from Horizontal, the round has to penetrate 120mm. Beyond this, as the angle of slope increases, something called bending stress is applied to the penetrator; which, at extreme slope drastically reduces the penetration.

In more recent times APDS rounds have been given some new technology to increase their effectiveness. APFSDS adds Fin Stabilized to the middle of the name. Simply, fins are added to the dart to make it fly straighter and farther. Most modern penetrators arc made of Tungsten, but some, such as the APFSDS-DU are made with Depleted Uranium. This Uranium is very dense, the denser or heavier the bullet, the more energy or force it has when it hits the armor. Depleted uranium ammo generally gives the best penetration and really doesn't glow in the dark very much, honest, the Army said so. A -T for Tracer, after the name of the means that a small flare is in the tail of the round, allowing the shooter to see where it goes.

A totally different type a round is the HEAT High Explosive Anti Tank round. First employed in W W II, this round uses chemical energy to burn through the armor. When the round hits, a chemical "jet" is formed that melts through the tank's armor; the molten "plasma" then splashes around inside the tank usually causing a massive fire.

This is the type of warhead that most anti-tank missiles use. The shape of the jet is important as is the shape of the cone inside the warhead that shapes the jet. In order to achieve ideal jet formation, many modern HEAT rounds have a stand off probe protruding from the front of the warhead. Sloped or reactive armor deforms the jet and decreases penetration. Spaced armor sets off the warhead too soon; causing, the warhead to burn out before the armor is penetrated. The "fuel" in the warhead burns at typically between 25,000 and 32,000 feet per second, making the brief burn time one of the limiting factors for this type of round. This round can have a low muzzle velocity, meaning low barrel wear and lower recoil for the gun, and is the primary anti-tank round of most field guns and howitzers. The lower velocity means lower range and accuracy. Penetration is the same at all ranges for any given round as penetration is determined by the amount of chemical Fuel carried by the round.

The last type of ammo that 1 will mention is HESH-High Explosive Squash Head or HEP-High Explosive Plastic; this round uses a plastic explosive that adheres to the armor on impact and then detonates sending a shock wave through the armor. When the shock wave reaches the inside surface of the armor, it causes spalling, or tiny pieces of armor to break away and bounce around the inside of the tank. Crews don't like it when that happens because they tend to get perforated. HESH is defeated by spaced armor, the shock wave doesn't make it to the inside of the tank, and by reactive armor. The advantage of HESH is that it is not effected by armor angle, and it can be used as a high explosive round against infantry.

Effects of Penetration

Going back to that 105mm gun at the beginning of this article, when its APDS round penetrates a target, horrible things happen. The penetrator brakes up into several hundred pieces, a few hundred of these can way as much as an ounce each. These pieces fly around the inside of the tank at initially over 2000 feet per second. And have an effect on the crew that is similar to machine gunning them from all sides at the same time. If anyone survives this, they must hope that these pieces do not ignite hydraulic fluid (a serious problem in the M60 series tanks) or set off ammunition.

The HEAT round is a little different, it hits the armor, the fuse ignites the chemical warhead and the jet burns through the armor. So the crew suddenly has a splat of molten warhead and armor at a few thousand degrees inside the tank with them. The immediate effect of the splat is more localized than that of the APDS round, but usually there is a catastrophic fire that kills crewman who survive the initial penetration.

The erect of HESH is similar to the APDS round mentioned above, but there is far less debris bouncing around the tank, and seldom is there a fire.

Beyond killing the crew or even penetrating the armor, a round can render the tank combat ineffective. Tracks, transmissions, or engines can fail due to the tremendous energy transfer of an impact. Gun laying equipment can be jammed of knocked out of calibration. And the crew can be simply knocked senseless by the concussion. 

Ultimately, understanding the math regarding these weapons is beyond many of us, but understanding the methods, applications, and effects are not. Thank you for reading and 1 hope you were able to find this informative, if not terribly exciting.