The rockets that fell on a military base in Iraq did not distinguish between soldiers and contractors.

Nawres Hamid, a U.S. contractor working as an interpreter, was killed in the Dec. 27 attack by an Iranian-backed militia that also injured American troops, prompting retaliatory strikes that edged the United States and Iran closer to open conflict.

Hamid’s death illuminated the proliferation of contractors at U.S. bases worldwide over the past two decades, a presence that camouflages the true cost of war, according to a study on the commercialization of the U.S. war effort.

About 53,000 U.S. contractors were in the Middle East last year, compared with 35,000 U.S. troops, according to a study by Boston University and Brown University. That ratio was 1 to 1 during the height of troop levels in Iraq in 2008. And since 2001, an estimated 8,000 contractors for U.S. companies have died on duty in the Middle East. That figure is 1,000 more than U.S. troops who have been killed.

Many of the contractors killed were foreign nationals. That has led to a double exploitation of using foreign workers for dangerous jobs and paying them less than U.S. employees earn, said Heidi Peltier, part of the Costs of War project at Boston University and Brown University.

“It hides the human cost and makes war more politically palatable,” Peltier told The Washington Post.

The reliance on defense contractors, once touted as a way to reduce costs and improve quality of services for the military, has instead led to a glut of spending, the study concluded. More than half of the defense budget last year — $370 billion — was spent on all contractor efforts, from weapons to services, according to the study.

There is also a concern that the reliance on private military contractors has blunted the public’s understanding of the human cost of America’s unprecedented long-term deployments.

“You don’t see yellow ribbons around trees for contractors,” said Mark Cancian, a defense budget expert for the Center for Strategic and International Studies. “All these touching scenes of the military service member coming home and scooping his kids up at the airport, you never see that for contractors.”

The Pentagon did not return a request for comment.

Analysts say the reliance on private military contractors started during the Clinton administration, when U.S.-based companies played a prominent role in training and equipping the Croatian military.

But the contractor economy expanded drastically after the Sept. 11 terrorist attacks, as companies found a lucrative business on sprawling bases in Iraq, Afghanistan, Kuwait and other nations. The George W. Bush administration relied heavily on private military corporations to support a fast scale-up in the U.S. military presence in Iraq as the security situation worsened there.

Reports of abuses perpetrated by armed private security forces working for companies like Blackwater created a public perception of contractors as irresponsible mercenaries, stirring a broader conversation about oversight and authorities.

But most contractors deployed to war zones have been engaged in the mundane yet often dangerous work of logistics and supply. U.S. contracting companies such as DynCorp and Triple Canopy have handled laundry, run dining facilities, operated bus lines, built tents and housing units, transported fuel and water, provided base security officers, and carried out other duties.

Many conservative think tanks and corporations pushed the idea of contractors absorbing duties the military historically performed for itself to lower costs and improve quality, the study concluded.

But often the opposite occurred, according to the study. Companies driven by no-competition bids have little incentive to cut costs.

Companies further boosted profits by hiring host country citizens or third-country nationals paid a fraction of U.S. wages, Peltier said, which fostered abuse and poor working conditions.

Those numbers don’t tell the whole story, said Steven Schooner, a professor of government procurement law at George Washington University. Contractors don’t earn taxpayer-funded education or health-care benefits that service members and veterans receive, he said, so some long-term costs are avoided.

However, the U.S. government doesn’t openly acknowledge or track deaths or injuries among contractors, Schooner said, and it is unknown how many of the fatalities were U.S. citizens or foreign nationals.

“There is a perverse incentive by the White House and the Defense Department to not have this information in the public domain,” he said.

The increasing involvement of numerous companies opened opportunities for fraud, corruption or shoddy products.

Companies have consistently been docked for charging exorbitant prices and violating contract terms. Nearly every company responsible for the Defense Department’s subsistence prime vendor program, a privatized food supply contract, has settled federal fraud allegations.

Taxpayers, the contractors themselves and U.S. troops sometimes paid the consequences. In 2008, Army Staff Sgt. Ryan Maseth was electrocuted in a shower built by KBR, and his death was among others blamed on poor work. The Army found that contractors and government employees “breached their respective duties of care,” but no criminal charges were filed.

Cancian, the CSIS analyst, said deployed military contractors are viewed as a significant and permanent part of the U.S. national security apparatus. Their presence on the battlefield has made long-term deployments more politically acceptable, he said.

“I don’t think this masks the cost of war … all the figures are out there,” Cancian said. “The difference is the public doesn’t care as much about contractors as much as it does about military personnel, and therefore is more willing to let military operations continue.”

Hamid’s death may be among the exceptions. Shortly after, President Trump tweeted that Iran had killed an American contractor and would be “held fully responsible.”

In the conflagration that followed. Maj. Gen. Qasem Soleimani, commander of the Quds Force of Iran’s Revolutionary Guard Corps, was killed in a U.S. airstrike.

Hamid, a naturalized U.S. citizen, was not eligible for burial in Arlington National Cemetery, where U.S. service members are interred. Instead, he was laid to rest at the Greater Sacramento Muslim Cemetery, in a funeral paid for by his employer, a Virginia-based defense contractor called Valiant Integrated Services.