Those services “fall within the existing mission” of the Office of Security Assistance-Iraq, “which is to help build institutional capacity of Iraq’s security ministries,” Defense Department spokesman Commander Bill Speaks said in an email.

The rapid advance of Islamic State militants in Iraq in recent months has spurred the deployment of almost 1,000 American troops to protect U.S. diplomatic facilities in Iraq’s capital Baghdad and the northern city of Irbil, in the semi-autonomous Kurdistan region.

Almost 100 additional servicemembers are there as advisers with the Office of Security Assistance–Iraq, and civilian advisers may not be far behind.

President Barack Obama last month authorized airstrikes against Islamic State militants, who have overrun large swathes of Iraq, when their advances threatened U.S. personnel in Baghdad and Irbil. But he has ruled out deploying ground combat units to Iraq less than three years after bringing the last of U.S. forces home from there.

Analysts say hiring contractors is a way to avoid deploying such forces.

David Johnson, a former Army lieutenant colonel who is executive director of the Center for Advanced Defense Studies in Washington, said contractors aren’t considered “boots on the ground” in conflict zones.

“The government always seeks to minimize boots on the ground to reduce domestic political risk,” he said in an email. “The American people and media do not consider a paid contractor to represent them in the same way that they do a soldier.”

Using contractors, who, most studies show, are cheaper than soldiers, trims the official presence and still accomplishes the logistical and security objectives, he said.

Defense contractors have plenty of experience in Iraq. During the U.S. occupation, thousands of armed security contractors and support personnel worked alongside foreign and Iraqi troops to help stabilize the country.

U.S. Central Command public affairs director Air Force Col. Patrick Ryder said in an email that the notice posted by the Army last month merely seeks to roll over a contract for civilian mentors and advisers in Iraq that has existed since 2012.

“The basic services being requested (go) back… to when there was a significant U.S. military presence in Iraq,” he said.

The contract is not a vehicle to increase U.S. presence in Iraq while avoiding the deployment of additional military forces or “boots on the ground,” he said.

Allison Stanger, a professor of international politics and economics at Middelbury College and author of a book on wartime contracting, said new Pentagon contracts for Iraq differ from security contractors hired by the State Department, which is seeking support “for a diplomatic mission, not a military one.”

“When the Pentagon does the same, it is another matter,” said Stanger, author of the book: “One Nation Under Contract: The Outsourcing of American Power and Future of Foreign Policy.” “In the era of contractors wars, there are many ways to avoid putting boots on the ground, while committing significant U.S. resources and actually being very much militarily involved.”

Michael O’Hanlon, of the Brookings Institute, said the U.S. government has employed as many contractors as it has deployed troops in Iraq and Afghanistan.

“As the political premium seems always to be placed on how many troops we have abroad, the pressure to have contractors do as much as possible only grows,” he said in an email.

Incidents such as the killing of civilians by Blackwater employees in Baghdad in 2007 remind policymakers of the dangers of having contractors as trigger pullers, but the pressure to minimize troop deployments means the ratio of contractors to troops may grow, he said.

Contractors are carrying a greater share of the load in Afghanistan these days as well. The U.S. plans to reduce the number of troops deployed there to fewer than 10,000 by year’s end but, according to a Congressional Research Service report, the number of contractors in Afghanistan ballooned to 108,000 last March at a time when 65,700 U.S. troops were there.

Johnson said vast numbers of contractors would likely remain in Afghanistan as troop levels declined.

The contractors provide services that local nationals wouldn’t be able to sustain in an impoverished, illiterate country, he said.

And while the four Blackwater guards on trial for the deaths of 14 of the victims claimed they believed they were under attack by an insurgent car-bombing attempt, no weapons or explosives were found on any of the dead Iraqis, despite an extensive FBI investigation. Instead, the official US investigation led to three men facing manslaughter charges, one accused of murder, and a fifth admitting manslaughter of other victims and testifying against his former colleagues.

But the 12 jurors who sat through harrowing evidence from victims and their relatives were not asked to assess the proportionality of the response. Like so many controversial encounters with security forces the world over, the crux of case is not whether the dead Iraqis posed a threat to the Blackwater convoy, but whether the guards’ belief that they did was a reasonable one.

From the perspective of soldiers working in hostile environments – whether as contractors or in the military – the distinction is a crucial protection and something that will have weighed heavily on the minds of a jury that included several veterans and US government employees. Other Blackwater employees – also working as guards for the US State Department – had been hit by a roadside bomb elsewhere in the city earlier that day.

Yet remarkably little evidence was presented to justify the guards’ ultimately false belief that the vehicles in Nisour Square posed a similar threat.

Both the prosecution and defence teams agreed that the primary reason for the guards thinking the convoy was about to be blown up was they had seen a white Kia sedan rolling toward them in what they claimed was a suspicious manner.

Defence lawyers allege the car was moving relatively fast and the guards shot at its engine block first to disable it, before killing the occupants. Prosecution lawyers allege the occupants – who turned out to be a medical student and his mother – were shot first and the car rolled forward slowly once the driver was dead because it was an automatic and his foot was off the brake.

The main alternative evidence presented to support the theory of self-defence concerned reports from some in the convoy that they had heard the sound of AK-47 gun fire and concluded it must have come from insurgents firing on the convoy.

Though this was not corroborated by any Iraqi witnesses, defence lawyers argued the theory was supported by a handful of AK-47 bullet casings found near the scene and several small dents on the Blackwater armoured vehicles and a leaking radiator that could have been caused by incoming rounds.

Prosecution lawyers argue that the damage was more likely to have been caused by fragments from the grenades that the guards were using and that bullet casings were a common sight on the streets of Baghdad at the time.

As justification for the killing of 14 unarmed civilians, several of whom appear to have been shot in the back allegedly while trying to flee the scene, such evidence may appear painfully thin. But jurors asked to convict the four defendants – Nicholas Slatten, Paul Slough, Evan Liberty and Dustin Heard – need only reasonable doubt to acquit in such circumstances.

Since an earlier attempt to try the same case collapsed when a judge questioned the way the defendants were initially interrogated, for the many Iraqis enraged by the incident, this may be the last chance to hold the men accountable.