BAGHDAD, Iraq -- For American military police patrolling the streets of Baghdad, the scariest thing about this war is that they seldom control their contact with the enemy. That contact normally involves the detonation of a roadside bomb, car bomb, or rocket-propelled grenade that comes out of nowhere, fired by insurgents who quickly slip away. It is a contact common to warfare since medieval times, brutal and instantaneous: metal smashing against metal. And that's why MPs rolling out of the gates of Camp Graceland, on the south side of Baghdad, feel safest in a heavily armored experimental vehicle that is...