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Brian Castner combed over the armored vehicle, mostly intact aside from entry and exit holes rimmed with molten copper that had since cooled.

The U.S. soldiers who had been inside were evacuated near Kirkuk that summer in 2006, leaving the Air Force bomb technician alone with the vehicle. Pools of blood simmered under the Iraqi sun.

The U.S. killing of Maj. Gen. Qassem Soleimani, the head of Iran’s elite Quds Force, has refocused attention on Soleimani’s legacy in Iraq, where sophisticated weapons and tactics he oversaw menaced U.S. troops for years, leaving a trail of dead and wounded service members.

The vehicle that Castner inspected was eviscerated by an explosively formed penetrator (EFP), a weapon of Iranian engineering that was salted across battlefields wherever Iranian-backed Shiite militias and fighters gathered, such as Kirkuk and Baghdad’s Sadr City, Castner said.

The weapons, compact but potent, are deployed against armored vehicles in a way similar to traditional IEDs but are much deadlier and more effective, Castner said. But they are also more complex and difficult to produce.

Shaped like a coffee can but a little smaller, with a slightly concave end, the device is packed with plastic explosives that turn a copper plate into molten slugs that barrel through several inches of armor, sending elongated shards tumbling through bodies and vehicles, and producing entry and exit holes similar to gunshots.

“They were really bad,” Castner said, and by far the most-dreaded explosive device he encountered because of their deadly efficiency.

EFPs killed at least 196 U.S. troops and wounded nearly 900 between 2005 and 2011, defense officials revealed in 2015, and Castner said a high number of amputations throughout the war were the direct result of the weapons. In the 2006 attack, slugs took both legs off a soldier and one from a gunner, he wrote in his memoir, “The Long Walk.”

The copper slugs, which form into a tadpole shape, can reach Mach 6, or 2,000 meters per second. By comparison, a .50-caliber round fired from a sniper rifle has a muzzle velocity of less than 900 meters a second.

Shaped charges have roots in World War II, but their variants, EFPs, were employed by Hezbollah as early as the 1990s against Israelis before migrating to Iraq in 2004, according to the U.S. Army’s history of the war.

Soleimani’s Quds Force provided EFP training and logistics to militants in Iraq, along with far-reaching supply routes and factories inside the country, the history said, where knowledge and tips on their construction filled CD-ROMs circulated among bomb-makers.

The United States spent billions of dollars to curtail the threat of IEDs, but the killing continued long after measures such as radio signal jammers and other equipment saturated the country. The number of EFP attacks peaked in 2008, the Military Times reported.

Iran was responsible for at least 603 U.S. deaths in Iraq, defense officials have said, or about a sixth of all fatalities. Hundreds of EFP victims and their family members are seeking damages from Iran in federal court for its role in deploying the weapon, the Times reported.

“We honestly did not believe that these guys were capable of doing this kind of stuff,” one senior defense official said in 2007, speaking of the Iranians. “We underestimated them.”