Rocket propelled grenades are explosive projectiles currently used in modern warfare to attack or destroy enemy targets from a distance. RPGs have their origins in mortars, which have been used as weapons of siege ever since the 1500s. Basically, a mortar is a metal tube aiming into the air, inside which mortar shells are dropped. As the shell falls towards the lower part of the metal tube, it triggers an explosive charge that propels it upwards.
As the projectile exits the tube it describes a parabolic trajectory into the air, before exploding in contact with the target. Although the distance and the orientation of the shell can be controlled to some extent, mortars are known to be extremely inaccurate. Another downside is that much of the energy of the explosive charge propelling the shell is used to get it high into the air, which affects their range. Nevertheless, they are popular even today and are still used in modern warfare.
The problems with mortars can be easily solved once the means of propelling the shells are improved and the metal tubes are brought from an upstanding position to a direction pointing towards the target, so that the shells travel in a straight line, to enhance range and accuracy. Rocket propelled grenades
An RPG is basically a hybrid between a rocket and a mortar. As is the case with mortars, RPGs consist of two different devices, the explosive projectile (grenade) and the device used to launch it. Unlike their predecessors, RPGs are no longer placed upwards on the ground but are brought into a near horizontal position, enabling them to be mounted on a combat vehicle or to be carried on the shoulder. This also implies that they must be much lighter than mortars.
The launch tube is opened at both ends, so that the loading process can be done from the back. At the same time, the back opening allows the ignited gases of the propelling system to exit into the atmosphere, thus producing less recoil when the grenade is fired. Once the projectile leaves the metal tube, it travels straight towards the target and explodes upon impact. Safety features on modern RPGs however, enable the detonation of the exploding charge to take place after a given amount of time, just in case the impact does not occur or the impact detonator is not functioning properly.