What are military contractors?
They are the legions of civilian workers who are hired to provide support tasks for the military. Some are former soldiers, but the vast majority of them don't carry weapons. The jobs they do range from building barracks and staffing cafeterias to guarding diplomats and intelligence gathering. Armies have always relied on such support staff. But since 9/11, U.S. reliance on contractors has metastasized. In the Iraq conflict, the U.S. employed 155,000 contractors — about the same as the number of U.S. soldiers there — while toward the end of the Afghanistan War, 207,000 contractors supported 175,000 soldiers. Even now, there are some 1,600 military contractors still working for the U.S. in Iraq. It's unclear what role they're playing and whether any of them will directly join in the fight against ISIS. For contractors paid by the U.S., "it's technically illegal to operate offensively or to take part in combat," said Molly Dunigan of the RAND Corp. "But lines blur quickly in the fog of war."

Why did the U.S. shift to contractors?
The practice really took off under President George W. Bush, as the U.S. fought simultaneous wars in Iraq and Afghanistan, stretching the supply of soldiers. Defense Secretary Donald Rumsfeld also believed the Pentagon could save money by bypassing government workers and contracting support tasks out to the private sector. Halliburton, DynCorp, Blackwater, and other companies were paid $200 billion to build infrastructure, feed and support troops, and provide security in Iraq and Afghanistan.

Did they do a good job?
They did a tremendous amount of work, but not without inefficiencies of their own. The Commission on Wartime Contracting, established by Congress in 2008 to sift through the accounts, found that up to $60 billion — or about one of three dollars spent — was lost to waste or fraud. The major contractors subcontracted out parts of their contracts to other firms, which then sub-subcontracted to still other firms. Some companies listed salaries for phantom employees or billed for services not rendered. An audit of just four invoices out of 129 submitted by Aecom Government Services found $4 million in overbilling out of $30 million in charges — including one charge of nearly $200 for a bag of washers that cost $1.22. Worse than the fraud, though, were allegations that some of the armed contractors unjustly used their weapons against Iraqi civilians.

How did that happen?
In Iraq, Blackwater provided security for the State Department, protecting the U.S. Embassy and other diplomatic sites that in an earlier era would have been guarded by Marines. In 2007, after reports that armed Blackwater staffers were behaving arrogantly and abusing Iraqi civilians, the State Department sent investigators to Baghdad. They found numerous flagrant violations. Blackwater's manager in Iraq, Daniel Carroll, demanded that the investigators leave, telling one he could kill him and get away with it because Iraq was a war zone. Just weeks later, Blackwater contractors opened fire with automatic weapons in Baghdad's Nisour Square, killing 17 Iraqis, including a child. Last month, at a trial in federal court in Washington, one Blackwater employee was convicted of murder and three of manslaughter for those deaths.

Will contractors be used against ISIS?
Yes — in one role or another. The bases in Qatar and elsewhere that are the source of U.S. airstrikes require significant support staff to provide food and do the maintenance and cleaning of military facilities. President Obama has been adamant that there will be no U.S. military "boots on the ground" to fight the ISIS insurgency in Syria and Iraq. But contractors can also be hired to train moderate Syrian rebel factions or Iraqi Kurdish factions in the use of the weaponry the U.S. has pledged to supply. The real question is whether contractors will be hired as mercenary warriors.

Is that under consideration?
Erik Prince, the Blackwater founder who now heads a military services company called Frontier Services Group, is openly advocating the idea. He said since the U.S. won't send troops to fight ISIS, it should hire "a multibrigade-size unit of veteran American contractors" to "serve as the pointy end of the spear" for local fighters. While the administration is unlikely to publicly announce hiring mercenaries, President Obama did say that the fight against ISIS would be like the action in Somalia, where the U.S. has a "strategy of taking out terrorists who threaten us while supporting partners on the front lines." Those partners in Somalia include heavily armed, private U.S. security firms. The contracting firms already in Iraq, such as Triple Canopy, are advertising for positions such as "defense marksman," for which an applicant must be a trained sniper. When the U.S. pulled most of its troops out of Iraq, "it made us even more dependent on contractors for security," says former congressman Christopher Shays, who co-chaired the Commission on Wartime Contracting. "The one thing that's a given: We can't go to war without contractors, and we can't go to peace without contractors."

The uncounted American deaths
About as many contractors working for the U.S. have been killed in Afghanistan and Iraq as U.S. troops, but those deaths generally are ignored in assessing the cost of the wars. As of October 2014, 6,838 troops had been killed in the two conflicts, while the estimated number of contractors killed was some 6,800. Tens of thousands of additional contractors have been injured, with some losing limbs or suffering other permanent disabilities. These people don't get veterans' benefits, and a group of them have filed a class action suit against Blackwater, KBR, DynCorp, and other firms and their insurers alleging that they were denied medical care after being injured in war zones. Steven Schooner, a former White House military procurement official who studies contractor policy at George Washington University, said Americans need to be aware that "their government has increasingly delegated to the private sector the responsibility to stand in harm's way and, if required, die for America."