A heavy machine gun (HMG) is significantly larger than light, medium or general-purpose machine guns. HMGs are typically too heavy to be man-portable (carried by one person) and require mounting onto a weapons platform to be operably stable or tactically mobile, have more formidable firepower, and generally require a team of personnel for operation and maintenance.
There are two classes of weapons generally defined as HMGs:
The .50 BMG (.50 Browning Machine Gun), also known as 12.7×99mm NATO, and designated as the 50 Browning by the C.I.P., is a .50 in (12.7 mm) caliber cartridge developed for the M2 Browning heavy machine gun in the late 1910s, entering official service in 1921. Under STANAG 4383, it is a standard service cartridge for NATO forces. The cartridge itself has been made in many variants: multiple generations of regular ball, tracer, armor-piercing (AP), incendiary, and saboted sub-caliber penetrator rounds. The rounds intended for machine guns are made into a continuous ammunition belt using metallic links.
The .50 BMG cartridge is also used in anti-materiel rifles. A wide variety of ammunition is available, and the availability of match grade ammunition has increased the usefulness of .50 caliber rifles by allowing more accurate fire than lower-quality rounds.
Hit-and-run tactics are a tactical doctrine of using short surprise attacks, withdrawing before the enemy can respond in force, and constantly maneuvering to avoid full engagement with the enemy. The purpose is not to decisively defeat the enemy or capture territory but to weaken enemy forces over time through raids, harassment, and skirmishing and limiting risk to friendly forces. Such tactics can also expose enemy defensive weaknesses and achieve a psychological effect on the enemy's morale.
Hit-and-run is a favored tactic where the enemy overmatches the attacking force and any sustained combat is to be avoided, such as guerrilla warfare, militant resistance movements, and terrorism. However, regular army forces often employ hit-and-run tactics in the short term, usually in preparation for a later full-scale engagement with the enemy when and where conditions are more favorable. Examples of the latter include commando or other special forces attacks, reconnaissance-in-force, or sorties from a fortress, castle, or other strongpoint. Hit-and-run tactics were also used by the lightly armed horse archers, typical of the Eurasian steppe peoples, who excelled at them. That holds especially true for such troops that were not part of a large army (such as scouting parties), but it was common to see them employed in such a way even as part of a major force.
A tank gun or tank cannon is the main armament of a tank. Modern tank guns are high-velocity, large-caliber artillery capable of firing kinetic energy penetrators, high-explosive anti-tank, and cannon-launched guided projectiles. Additional weapons, such as anti-aircraft guns, heavy machine guns and rocket launchers can also be mounted to tanks.
As the tank's primary armament, they are almost always employed in a direct fire mode to defeat a variety of ground targets at all ranges, including dug-in infantry, lightly armored vehicles, and especially other heavily armored tanks. They must provide accuracy, range, penetration, and rapid fire in a package that is as compact and lightweight as possible, to allow mounting in the cramped confines of an armored gun turret. Tank guns generally use self-contained ammunition, allowing rapid loading (or use of an autoloader). They often display a bulge in the barrel, which is a bore evacuator, or a device on the muzzle, which is a muzzle brake.
The M2 machine gun or Browning .50-caliber machine gun (informally, "Ma Deuce") is a heavy machine gun that was designed near the end of World War I by John Browning. While similar to Browning's M1919 Browning machine gun, which was chambered for the .30-06 cartridge, the M2 uses Browning's larger and more powerful .50 BMG (12.7 mm) cartridge. The design has had many designations; the official U.S. military designation for the infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It has been used against infantry, light armored vehicles, watercraft, light fortifications, and low-flying aircraft.
The gun has been used extensively as a vehicle weapon and for aircraft armament by the United States since the 1930s. It was heavily used during World War II, the Korean War, the Vietnam War, the Falklands War, the Soviet–Afghan War, the Gulf War, the Iraq War, and the War in Afghanistan. It is the primary heavy machine gun of NATO countries and has been used by many other countries as well. U.S. forces have used the M2 longer than any other firearm except the .45 ACP M1911 pistol, which was also designed by John Browning.
An improvised fighting vehicle is an ad hoc combat vehicle resulting from modified or upgraded civilian or military non-combat vehicle, often constructed and employed by civilian insurgents, terrorists, rebels, mobsters, guerrillas, partisans, drug cartels, criminal organizations or other forms of non-state militias and irregular armies. Such modifications usually consist of grafting improvised armour plating and fixed crew-served weapons such as heavy machine guns or antiaircraft autocannons mounted onto the back of a utility vehicle or pickup truck.
Various militias and official militaries have improvised such vehicles ever since the introduction of the first automobiles into military service. During the 1910s and 1920s, the absence of a doctrine for the military use of automobiles or of an industry dedicated to producing them led to a great deal of improvisation in the creation of early armored cars and similar vehicles.