A roadside bomb that killed an American soldier in Iraq earlier this month was of a particularly lethal design not seen in six years, and its reappearance on the battlefield suggests that U.S. troops could again be facing a threat that bedeviled them at the height of the insurgency here, U.S. military officials said.
The device was of a variety known as an explosively formed penetrator, or EFP, according to initial investigations, a weapon notorious for its destructive and deadly impact on armored vehicles and the service members inside them, two U.S. military officials said.
EFPs were among the most lethal weapons faced by U.S. forces before a troop withdrawal in 2011. The devices were considered a hallmark of the Iranian-backed Shiite militias battling the U.S. occupation after the toppling of Saddam Hussein. But the technology used to make them proliferated, and cruder versions were also deployed by Sunni militants.