American and Iraqi forces uncovered an assembly area for the powerful roadside bombs known as explosively formed projectiles, the statement said.

Only a small fraction of the roadside bombs used in Iraq are explosively formed penetrators.

The most lethal development is the use of the "explosively formed penetrators," which pierce armor and stay intact when they explode.

The four men are suspected of helping shuttle into Iraq a deadly type of homemade bomb called an explosively formed penetrator, the military said.

Ordnance experts at the scene found another bomb, a particularly deadly type called an explosively formed projectile, that had not been detonated, the military said.

The properties of metals under hypervelocity have been integrated with weapons, such as explosively formed penetrator.

Due to its high density, shaped charge and explosively formed penetrator liners have been constructed from tantalum.

According to one military official, reports of the "explosively formed penetrator," as the weapon is known, first surfaced in late 2003.

A relatively new type of remotely-detonated mine, the explosively formed penetrator was used with some success against American armored vehicles.

See also explosively formed projectiles for a variety of military applications of the same kind of technology.