Former Air Force airmen are speaking out against America’s use of drone warfare, calling the military drone program “morally outrageous” and “one of the most devastating driving forces for terrorism and destabilization around the world.”

In interviews with NBC News, three former servicemen — who together have 15 years of military drone experience — decried the civilian cost of drone strikes and called on President Obama to “turn this around” before he leaves office.

“We were very callous about any real collateral damage,” said Michael Haas, 29, who worked as both a drone operator and instructor. “Whenever that possibility came up, most of the time it was a ‘guilt by association’ or sometimes we didn’t even consider other people that were on screen.”

Related: Terror Suspects Are Frequent Targets of U.S. Drones

Alongside a former drone operator who was not available to speak with NBC News, the three self-described whistleblowers also wrote a letter to President Obama, Defense Secretary Ash Carter, and CIA Director John Brennan in which they link drone strikes to the rise of ISIS and to the recent attacks in Paris. For terrorists, they wrote, drone attacks are "a fundamental recruiting tool similar to Guantanamo Bay.”

The Air Force, in a statement sent to NBC News, said: "Our remotely piloted aircraft operators perform a critically important mission that contributes significantly to national defense and global security." The statement did not address the former airmen’s claims directly.

American drone strikes have increased exponentially under President Obama; in Pakistan alone, the current administration has launched 370 strikes compared to the Bush administration’s 51, according to the Bureau of Investigative Journalism, which tracks the attacks.

Add Somalia and Yemen (using New America Foundation data), and President Obama has launched 894 percent more drone strikes than did his predecessor.

Combined, drone strikes on Pakistan, Somalia and Yemen have killed 2,736 to 4,169 militants, according to the New America Foundation.

Meanwhile, those strikes have also killed hundreds of civilians. Estimates range from 488 to 1,071, according to the Bureau of Investigative Journalism.

“We witnessed gross waste, mismanagement, abuses of power, and our country’s leaders lying publicly about the effectiveness of the drone program,” the four men wrote in their letter.

Their lawyer, Kathleen McClellan, called their open opposition a "historic moment.”

“This is the first time this many people who served in the drone program are speaking out,” she said in an interview with NBC News.

Stephen Lewis, 29, who controlled the cameras on the drones that helped guide Hellfire missiles into their targets, said he “drank [himself] to sleep” every night after getting home from work. “It was the culture there,” he said. “Everybody did something to take the edge off — to reform reality so you didn’t have to think about what you did.”

Cian Westmoreland, 28, who worked on communications infrastructure out of bases in Germany and Afghanistan, said he had nightmares “about kids or mothers dying and me trying to help them, and I couldn’t.

“I would just feel helpless. And I knew it was partially my fault,” he said.

Brandon Bryant, 30, was the former drone operator not available for an interview.

All four men say that they suffer from PTSD. Their representatives say they were all honorably discharged — and that they were offered reinstatement bonuses that ranged from $50,000 to $110,000.

Drone pilots "are professional and comply with applicable law, policies and adhere to very exacting procedures," the Air Force added. "Airmen are expected to adhere to established standards of behavior."

The Air Force is currently struggling to retain drone pilots and is losing more pilots than it is training, though it says "a great deal of effort is being taken" to "stabilize the force."

“The remotely piloted aircraft career field is under severe strain,” the Senate Armed Services Committee wrote in its May 2015 report.

Lewis remembers why he left. “Immediately after I took my first life,” he said, he told his superiors that “I didn’t belong there — I didn’t need to be there anymore.

“People think it’s a video game,” he said. “But in a video game you have checkpoints, you have restart points.”

With drones, “when you fire that missile, there’s no restart.”