I'm a veteran and lived in the Washington DC area through the Iraq war years and knew many, many contractors who worked in Iraq. When US military personnel take the field, their needs are cared for like no other army in history. The contractors do technical work and provide services to the forces, and some work with civilians doing civil engineering and relief work. This freed up the soldiers to patrol and fight as needed. Only a small percentage of these contractors you speak of were armed, and those that were provided security and didn't go on assault or reconnaisance operations. Most civilian contractors that died were killed in roadside IED explosions and by booby traps, just like most soldiers.