used for both defensive and guerrilla purposes. Anti-tank mines were also used extensively in Cambodia and along the Thai border, planted by Pol Pot's Maoist guerrillas and the Vietnamese army, which invaded Cambodia in 1979 to topple the Khmer Rouge. Millions of these mines remain in the area, despite clearing efforts. It is estimated that they cause hundreds of deaths annually to civilians. Rocket-propelled grenades Rocket-propelled grenades (RPGs) were used extensively during the Vietnam War (by the Vietnam People's Army and Viet Cong), Soviet invasion of Afghanistan by the Mujahideen and against South Africans in Angola and Namibia (formerly South West Africa) by SWAPO guerrillas during what the South Africans called the South African Border War. Twenty years later, they are still being used widely in recent conflict areas such as Chechnya, Iraq, and Sri Lanka. The RPG still remains a potent threat to armored vehicles, especially in situations such as urban warfare or jungle warfare, where they are favored by guerrillas. They are most effective when used in restricted terrain as the availability of cover and concealment can make it difficult for the intended target to spot the RPG operator. Note that this concealment is often preferably outdoors, because firing an RPG within an enclosed area may create a dangerous backblast. In Afghanistan, Mujahideen guerrilla fighters used RPG-7s to destroy Soviet vehicles. To assure a kill, two to four RPG shooters would be assigned to each vehicle. Each armored-vehicle hunter-killer team could have had as many as 15 RPGs per unit. In areas where vehicles were confined to a single path (a mountain road, swamps, snow, urban areas), RPG teams trapped convoys by destroying the first and last vehicles in line, preventing movement of the other vehicles. This tactic was especially effective in cities. Convoys learned to avoid approaches with overhangs and to send infantrymen forward in hazardous areas to detect the RPG teams. Multiple shooters were also effective against heavy tanks with reactive armor: The first shot would be against the driver's viewing prisms. Following shots would be in pairs, one to set off the reactive armor, the second to penetrate the tank's armor. Favored weak spots were the top and rear of the turret. The Mujahideen sometimes used RPG-7s at extreme range, exploded by their 4.5-second self-destruct timer, which translates to roughly 950m flight distance, as a method of long distance approach denial for enemy infantry and