Rocket-propelled grenade

A rocket-propelled grenade, also known colloquially as a rocket launcher, is a portable, reusable, unguided, shoulder-launched, anti-tank grenade launcher that launches rockets equipped with a shaped-charge 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, stabilized in flight with fins. Some types of RPG are reloadable with new anti-tank grenades, while others are single-use. RPGs are generally loaded from the front.
RPGs with high-explosive anti-tank warheads are very effective against lightly armored vehicles such as armored personnel carriers and armored cars. However, modern, heavily-armored vehicles, such as upgraded APCs and main battle tanks, are generally too well-protected 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 and other unarmored targets.
The term "rocket-propelled grenade" is a backronym from the Russian acronym РПГ, meaning 'hand-held anti-tank grenade launcher', the name given to early Soviet 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 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.
The first dedicated anti-tank artillery began appearing in the 1920s, and by World War II was a common appearance in most armies. In order to penetrate armor they fired specialized ammunition from proportionally longer barrels to achieve a higher muzzle velocity than field guns. Most anti-tank guns were developed in the 1930s as improvements in tanks were noted, and nearly every major arms manufacturer produced one type or another.
Anti-tank guns deployed during World War II were manned by specialist infantry rather than artillery crews, and issued to infantry units accordingly. The anti-tank guns of the 1930s were of small caliber; nearly all major armies possessing them used ammunition, except for the British Army, which had developed the Ordnance QF 2-pounder. As World War II progressed, the appearance of heavier tanks rendered these weapons obsolete and anti-tank guns likewise began firing larger calibre and more effective armor-piercing shells. Although a number of large caliber guns were developed during the war that were capable of knocking out the most heavily armored tanks, they proved slow to set up and difficult to conceal. The latter generation of low-recoil anti-tank weapons, which allowed projectiles the size of an artillery shell to be fired from a man's shoulder, was considered a far more viable option for arming infantrymen.

First shaped charge, portable weapons

The RPG has its roots in the 20th century with the early development of the explosive shaped charge, in which the explosive is made with a conical hollow, which concentrates its power on the impact point. Before the adoption of the shaped charge, anti-tank guns and tank guns relied primarily on kinetic energy of metal projectiles to defeat armor. Soldier-carried anti-tank rifles such as the Boys anti-tank rifle could be used against lightly-armored tankettes and light armored vehicles. However, as tank armor increased in thickness and effectiveness, the anti-tank guns needed to defeat them became increasingly heavy, cumbersome and expensive. During WW II, as tank armor got thicker, larger calibre anti-tank guns were developed to defeat this thicker armor.
While larger anti-tank guns were more effective, their weight meant that they increasingly were mounted on wheeled, towed platforms. This meant that if the infantry was on foot, they might not have access to these wheeled, vehicle-towed anti-tank guns. This led to situations where infantry could find themselves defenseless against tanks and unable to attack tanks. Armies found that they needed to give infantry a human-portable weapon to defeat enemy armor when no wheeled 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. 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 RPG.
Research occasioned by World War II produced such weapons as the American bazooka, British/Allied PIAT and German Panzerfaust, which combined portability with effectiveness against armored vehicles, such as tanks. The Soviet-developed RPG-7 is the most widely distributed, recognizable and used RPG in the world. The basic design of this RPG was developed by the Soviets shortly after World War II in the form of the RPG-2, which is similar in function to the bazooka and the Panzerfaust, though the rounds it fires lack a form of propulsion in addition to the launch charge.
Soviet RPGs were used extensively during the Vietnam War, as well as during the Soviet invasion of Afghanistan by the Mujahideen and against South Africans in Angola and Namibia by SWAPO guerillas during what the South Africans called the South African Border War. In the 2000s, they were still being used widely in conflict areas such as Chechnya, Iraq, and Sri Lanka. Militants have also used RPGs against helicopters: Taliban fighters shot down U.S. CH-47 Chinook helicopters in June 2005 and August 2011; and Somali militiamen shot down two U.S. UH-60 Black Hawk helicopters during the Battle of Mogadishu in 1993.
RPGs were used by militants to destroy "hundreds" of vehicles in the War in Afghanistan.

Design

The RPG warhead being used against tanks and other armor often has a shaped charge explosive warhead. A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to penetrate tank armor; typical modern lined shaped charge can penetrate steel armor to a depth of seven or more times the diameter of the charge, though greater depths of 10 CD and above have been achieved. Despite the popular misconception that shaped charges "melt" tank armor, the shaped charge does not depend in any way on heating or melting for its effectiveness; that is, the superplastic metal jet from a shaped charge impact on armor forms mainly due to a sudden and intense mechanical stress and does not melt its way through armor, as its effect is purely due to kinetic energy in nature.
An RPG comprises two main parts: the launcher and a rocket equipped with a warhead that follows a ballistic trajectory after the rocket motor has completed its burn. The most common types of warheads are high explosive and high-explosive anti-tank rounds. HE rounds can be used against troops or unarmored structures or vehicles. HEAT rounds can be used against armored vehicles. These warheads are affixed to a rocket motor and stabilized in flight with fins. Some types of RPG are single-use disposable units, such as the RPG-22 and M72 LAW; with these units, once the rocket is fired, the entire launcher is disposed of. Others are reloadable, such as the Soviet RPG-7 and the Israeli B-300. With reloadable RPGs, a new rocket can be inserted into the muzzle of the weapon after firing.
An issue that affected the earliest RPG weapon systems such as the German Panzerschreck was that rocket motor propellant could harm the operator. The weapon therefore featured a metal shield attached to the launch tube to protect the operator’s face from the blast. With later designs such as the RPG-7, the rocket exits the launcher with a low-powered gunpowder charge, and the main rocket motor then fires after the rocket has travelled. In some other designs, the propellant charge burns completely within the tube.
An RPG is an inexpensive way for an infantryman to safely deliver an explosive payload or warhead over a short distance with reasonable accuracy. Substantially more expensive guided anti-tank missiles are used at larger distances when accuracy or an overfly top attack are paramount. Anti-tank missiles such as the Malyutka can be guided by the operator after firing by sight, heat sensors or IR signatures; an RPG however is not guided towards the target. Nor can RPG rockets be controlled in flight after being aimed and launched. While the lack of active targeting technologies or after-firing guidance input can be viewed as a weakness, it also makes RPGs cheap and hard to defend against with electronic countermeasures or decoying. For example, if a soldier or other fighter launches an RPG at a hovering helicopter, even if the helicopter releases flares to confuse optical seekers, chaff to confuse radar, or engages in signal jamming, these will have no effect on an in-flight RPG warhead, even though these measures might protect against more sophisticated surface-to-air missiles.