The 41-year-old Russian rocket-propelled grenade — the RPG — was built as an anti-tank weapon, but it's been playing havoc with American helicopters.

Anti-American forces used RPGs to bring down two MH-47 Chinook helicopters fighting in the Shah-e-Kot area of Afghanistan on Monday. Seven U.S. soldiers were killed in the attacks and ensuing firefights. Several AH-64 Apache gunships were also hit by RPGs, but none crashed.

It's reminiscent of the Oct. 3, 1993, battle in Mogadishu, Somalia, when Somalis firing RPGs brought down a pair of UH-60 Black Hawk assault helicopters that had just delivered Rangers and Delta Force commandos. Eighteen U.S. servicemen were killed in the action, including members of both helicopter crews.

Rocket-propelled grenade, the official name for the RPG, precisely describes the weapon: it's a grenade, fired from a bazooka-like launcher, with a small motor. It is unguided, but a skilled operator can hit moving targets about 300 yards away. It's the explosive complement, almost as ubiquitous in guerrilla armies around the world as the AK-47 assault rifle.

The Soviets introduced the RPG-7 in 1961 to penetrate the armor of NATO tanks. Every squad of Soviet infantry had at least one RPG gunner. Today, more than 40 armies use them, and several countries, including Pakistan, are licensed to manufacture them. They are widely available on weapons black markets.

But guerrilla and terrorist forces, usually lacking access to modern heat-seeking anti-aircraft missiles, adapted them to shoot down low-flying helicopters and to conduct guerrilla attacks in cities.

Lester Grau, with the Army's Foreign Military Studies Office at Fort Leavenworth, Kan., described in 1998 how Afghan mujahedeen fighting the Soviets adapted the RPG to take down transport helicopters loaded with troops. His account is starkly similar to Monday's firefights.

"The mujahedeen found that the best anti-helicopter tactics were anti-helicopter ambushes," he writes in the magazine "Infantry." "The first variant was to identify likely landing zones and mine them. Then the mujahedeen would position machine guns and RPGs around the landing zone. As the helicopter landed, massed RPG and machine gun fire would tear into the aircraft."

Later in the war, the CIA supplied mujahedeen with heat-seeking Stinger missiles, which allowed them to bring down helicopters at greater altitudes. Some of these — along with their Russian counterparts, the SA-7 — are thought to be available to those fighting in eastern Afghanistan, as well.

Independence rebels in the Russian region Chechnya also have used RPGs against Russian forces in deadly city fighting in Grozny, the capital. They have hit Russian armored vehicles in the streets from rooftops and exposed basements.

"It is a proven, cheap killer of technology, which will continue to play a significant role — particularly when conventional forces are pitted against irregular forces," Grau writes. "The chances are, whenever a U.S. soldier is deployed to a trouble spot, the RPG-7 will be part of the local landscape."