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 chaff flares, engages in signal jamming or releases radar-fooling foil, these will have no effect on an in flight RPG warhead, even though these measures might protect against more sophisticated surface-to-air missiles. Warheads The HEAT (high-explosive anti-tank) round is a standard shaped charge warhead, similar in concept to those used in many tank cannon rounds. In this type of warhead, the shape of the explosive material within the warhead focuses the explosive energy on a copper (or similar metal) lining. This heats the metal lining and propels some of it forward at a very high velocity in a highly plastic state. The resulting narrow jet of metal can defeat armor equivalent to several hundred millimeters of RHA, such as that used in light and medium armored vehicles. 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 warhead detonates on impact or when the fuse runs out; usually the fuse is set to the maximum burn of the rocket motor, but it can be shortened for improvised anti aircraft purposes. Specialized warheads are available for illumination, smoke, tear gas, and white phosphorus. Russia, China, and many former Warsaw Pact nations have also developed a fuel-air explosive (thermobaric) warhead. Another recent development is a tandem HEAT warhead capable of penetrating reactive armor. So-called PRIGs (Propelled Recoilless Improvised Grenade) were improvised warheads used by the Provisional IRA. Effectiveness The RPG-29 uses a tandem-charge high-explosive anti-tank warhead to penetrate explosive reactive armor (ERA) as well as composite armor behind it. It is capable of penetrating MBTs, such as the American M1 Abrams, the older