A rocket-propelled grenade (RPG) is a shoulder-fired missile weapon that launches rockets equipped with an explosive warhead. Most RPGs can be carried by an individual soldier, and are frequently used as anti-tank weapons. These warheads are affixed to a rocket motor which propels the RPG towards the target and they are stabilized in flight with fins. Some types of RPG are reloadable with new rocket-propelled grenades, while others are single-use. RPGs are generally loaded from the front. RPGs with high-explosive anti-tank (HEAT) warheads are very effective against lightly armored vehicles such as armored personnel carriers (APCs) and armored cars. However, modern, heavily-armored vehicles, such as upgraded APCs and main battle tanks, are generally too well-protected (with thick composite or reactive armor) to be penetrated by an RPG, unless less armored sections of the vehicle are exploited. Various warheads are also capable of causing secondary damage to vulnerable systems (especially sights, tracks, rear and roof of turrets) and other unarmored targets. The term "rocket-propelled grenade" is a backronym from the Russian acronym РПГ (Ручной Противотанковый Гранатомёт, Ruchnoy Protivotankovy Granatomyot), meaning "handheld anti-tank grenade launcher", the name given to early Russian designs. History Predecessor weapons The static nature of trench warfare in World War I encouraged the use of shielded defenses, even including personal armor, that were impenetrable by standard rifle ammunition. This led to some isolated experiments with higher caliber rifles, similar to elephant guns, using armor-piercing ammunition. The very first tanks, the British Mark I, could be penetrated by these weapons under the right conditions. Mark IV tanks, however, had slightly thicker armor. In response, the Germans rushed to create an upgraded version of these early anti-armor rifles, the Tankgewehr M1918, the first anti-tank rifle. In the inter-war years, tank armor continued to increase overall, to the point that anti-tank rifles could no longer be effective against anything but light tanks; any rifle made powerful enough for heavier tanks would exceed the ability of a soldier to carry and fire the weapon. Even with the first tanks, artillery officers often used field guns depressed to fire directly at armored targets. However, this practice expended much valuable ammunition and was of increasingly limited effectiveness as tank armor became thicker. This led to the concept of anti-tank guns, a form of artillery specifically designed to destroy armored fighting vehicles, normally from static defensive positions (that is, immobile during a battle). The first