Rocket propelled grenade

A rocket-propelled grenade (often abbreviated RPG) is a shoulder-fired, anti-tank weapon system that fires rockets equipped with an explosive warhead. These warheads are affixed to a rocket motor and stabilized in flight with fins. Some types of RPG are reloadable, while others are single-use. RPGs, with some exceptions, are generally loaded from the muzzle.

RPGs with high explosive anti-tank warheads (HEAT) are very effective against armored vehicles such as armoured personnel carriers (APCs). However, heavily armored vehicles, such as main battle tanks, are generally too well armored to be penetrated by an RPG, unless weaker sections of the armor are exploited. Various warheads are also capable of causing secondary damage to vulnerable systems (especially sights, tracks, rear and roof of turrets) and other soft targets.

The term "rocket-propelled grenade" is strictly speaking a backronym; it stems from the Russian language РПГ or ручной противотанковый гранатомёт (transliterated as "ruchnoy protivotankovy granatomyot"), meaning "hand-held anti-tank grenade launcher", the name given to early Russian designs.

The RPG has its roots in the 20th century with the early development of the explosive shaped charge. Before the adoption of the shaped charge, anti-tank guns and tank guns relied primarily on kinetic energy to defeat armor. As tank armor increased in thickness and effectiveness, the guns needed to defeat them became increasingly heavy, cumbersome and expensive, meaning that infantry could find themselves defenseless against tanks. Armies found that they needed to give infantry the means to defeat enemy armor when no anti-tank guns were available, since anti tank rifles were no longer effective. Initial attempts to put such weapons in the hands of the infantry resulted in weapons like the Soviet RPG-40 blast effect hand grenade (here RPG stood for ruchnaya protivotankovaya granata, meaning hand-held anti-tank grenade). The later RPG-43 and RPG-6 used shaped charges, the chemical energy of their explosive being used more efficiently to enable the defeat of thicker armor; however, being hand thrown weapons, they still had to be deployed at suicidally close range to be effective. What was needed was a means of delivering the shaped charge warhead from a distance. Different approaches to this goal would lead to the anti-tank spigot mortar, the recoilless rifle and, from the development of practical rocketry, the rocket propelled grenade.

...
Wikipedia