This section is a quick discussion of the major types of main gun ammo in use. Most people think of a tanks main gun as being used only against other tanks. However, over the years many other types of ammo have been developed to increase the tanks versatility. Although not all of these types of ammo are used by th M1 series tank, they are still found throughout the world in other nations inventories.
APFSDS-T (Armor Piercing Fin Stabilized Discarding Sabot Tracer)
In the photo above you see a example of a kinetic energy round. This is a APFSDS-T round, commonly called a Sabot (Say-bo) round. This round has no explosive charge and is just a depleated uranium rod encased in a aluminum sabot to keep it the diameter of the bore. As you can see in the photo above, shortly after being fired the sabot separates and the projectile continues down range traveling at over a mile a second. This round destroys it's target by the sheer force of it's impact. It impacts with the force of a 11 ton truck moving at 70 MPH, concentrated into a area less than a inch in diameter. As it passes through the target the rounds kinetic energy in the form of velocity is converted to heat, causing ammo and fuel in the target to ignite. Also, it pushes a slug of armor through with it that breaks up and fragments inside the target, this adds to the destruction. This round is primarily for use against hard targets such as tanks and sometimes APC's. Against a soft target such as a truck it can have little effect, possibly causing no other damage than a small entrance and exit hole. The main drawback of this round is that the father is travels the more energy it loses due to air resistance. At very long ranges it is possible it may fail to penetrate, however the shock will cause the inside of the armor to shatter into fragments that travel around the inside of the target at high speed and wreak havoc with the crew and equipment. This effect is called spalling and will definitely get the crews attention!
HEAT (High Explosive Anti-Tank)
Shaped charge rounds have a explosive warhead and are commonly known as HEAT rounds. They contain a specially formed charge covered with a thin piece of metal. Due to the way the charge is formed, upon detonation a jet of hot gasses and molten metal is forced forward into the target at a very high speed. This jet burns/blasts it's way through the armor. This round has a advantage over the kinetic energy round in that velocity doesn't matter to it's effectiveness, it has the same amount of killing power at the end of it's flight as it does at the muzzle. Because of this most anti-tank missiles, due to their low velocity, use this type of warhead. One drawback is that the plasma jet is easily disrupted, defeating the rounds effectiveness. Spaced, composite, and reactive armor have all been developed to defend against HEAT rounds. During WWII chicken wire was even used with success against early HEAT rounds. The wire was laid across the tank several inches from the hull. When the round hit the wire it detonated and the plasma jet splashed against the hull without penetrating. Also spinning was found to degrade the plasma jet, thus most modern guns are smooth bore, relying on fins to stabilize the projectile. The HEAT-MP-T (High Explosive Anti-Tank Multi-Purpose Tracer) round used in the M1A1/M1A2 has a secondary fragmentation effect, causing it to act as a giant hand grenade, making it effective as a anti-personnel round.
MPAT (Multi-Purpose Anti-Tank)
MPAT is one of the newest rounds fielded ,and a very useful one. It gives the tank much better capabilities against helicopters. This round has 2 modes of operation which can be set by turning a dial on the tip of the round before it is loaded. In ground mode it acts like a conventional HEAT round and is effective against bunkers and lightly armored targets. In air mode a proximity fuze is activated and when it gets near a object such as a helicopter, it detonates. The resulting shrapnel is devastating to a lightly skinned target like a aircraft.
STAFF (Smart Target Activated Fire & Forget)
STAFF rounds are still in development and have not yet been fielded, however, the capability to fire this round has been incorporated into the M1A1 and M1A2 tanks. This round can be used to destroy dug in targets that normal rounds cannot reach. Once the round is fired it begins scanning for a large metal object. As the round passes over the target it fires a explosively formed penetrator through the thin top armor of the target.
APERS (Anti-PERSonnel)
This round is commonly known as Beehive and it is used against unprotected soldiers. Before being loaded, the range is set by turning a dial on the tip of the round. The round detonates before reaching the designated range, unleashing thousands of tiny wire darts. These darts effectively shred any personnel in a large area. This round was used extensively in the M48 tank in Vietnam. It has been reported that sometimes enemy soldiers were found literally nailed to trees and the ground. There is no 120mm version of this round for the M1A1/A2 but it is still capable of being fired by the 105mm gun on the M1.
HEP (High-Explosive Plastic)
HEP is basically a thin metal container filled with a explosive. Upon impact the shell splits and the round splats against the target, much like a wet snowball. A fuze in the base then detonates the charge causing the inside of the targets armor to spall. This round is also effective against bunkers, buildings, and other like targets. 105mm HEP is still in service for the M1, but there are no 120mm versions of this round.
WP (White Phosphorus)
Willey Pete is designed as a smoke round. The round contains white phosphorus which ignites and burns at a very high temperature when exposed to air. This makes it a very effective incendiary round. Once WP starts burning the only way to stop it is to remove it from air or let it burn itself out. Most conventional fire fighting techniques are not effective. These round are unique in that they must be stored standing up. If laid on their side for a long period the filler will settle out, affecting the rounds trajectory. Like APERS and HEP there are no 120mm versions of this round although 105mm is still in use.
HE (High Explosive)
HE is basically just a standard artillery shell. It has a explosive charge and a fuze that detonates the shell on contact with the target. This was the primary main gun round prior to the invention of the HEAT warhead during WWII. It has mostly been replaced by HEAT and HEP rounds.
Canister
A canister round's warhead breaks open upon leaving the muzzle releasing thousands of steel balls. This basically turns the main gun into a giant shotgun. This round was very effective against human wave attacks during the Vietnam War. It is no longer used by the U.S.
