During the Iraq War, there was a little bit more than one-to-one ratio of contractors to soldiers, he said. Now in Iraq, more than 30 percent (618) of the contractors are working in maintenance and logistics jobs. Nearly 20 percent (381) are translators and 13 percent (263) are in base support positions, according to the data. Contractors are also working in security, transportation, construction, communication support, training, management and administrative roles.

Nearly 70 percent of the contractors are American citizens, 20 percent are third-country nationals and the remaining are local Iraqis. The number of contractors the Pentagon can employ in Iraq is not capped, according to Col. Steve Warren, spokesman for Operation Inherent Resolve.

Many of the contractors in Iraq and neighboring countries are from well known warzone companies like KBR, DynCorp, and Fluor Corporation, the three firms hired by the Army’s Logistics Civil Augmentation Program, or LogCap. The Pentagon awards individual “task order” deals to these each time it needs to support troops overseas.

“It makes tailoring a unit much more responsive to the needs of the commander because you don’t have to try to rip people [with a trade specialty] from other installations,” Brennan said.

KBR, in a November presentation to investors, said its LogCap services work in Iraq “grew in the period with further growth possible.”

Besides the LogCap contractors, the Pentagon can award independent contracts, according to Andrew Hunter, a former Pentagon official who now director of the Defense-Industrial Initiatives Group at the Center for Strategic and International Studies, in Washington. In some instances, the Pentagon hires contractors already working for the government in order to speed up the process.

Even though U.S. troops withdrew fully from Iraq in 2011, many contractors stayed behind working at the American embassy or in logistical roles maintaining Iraq’s military equipment.

Congress ordered the Pentagon to provide detailed information about battlefield contractors following an incident in which private military contractors working for Blackwater USA killed 17 Iraqi civilians in Nisour Square in Baghdad in September 2007.

Not all contractors in the warzone are base guards, laundry workers or chefs. The CIA and other intelligence agencies still use contractors like the former Blackwater or $2.2 billion firm DynCorp and other for paramilitary services. The number of those contractors, some who are closer to the battlefield than the military advisors, is classified and unknown to the public.

U.S. Central Command, which oversees military operations in the Middle East, has sent Congress regular updates about the number of contractors being employed in Iraq and Afghanistan since August 2008. In July 2008, just following the 2007 troop surge, there were 162,428 Pentagon-funded contractors in Iraq, according to the data.