An MQ-9 Reaper drone at Creech Air Force Base in Nevada.
Credit: U.S. Air Force photo/Lance Cheung

In the final years of his nearly 30-year career in the U.S. Air Force, Slim spent 10 to 12 hours a day in a cool, dark room in the Arizona desert, stationed in front of monitors that beamed back aerial footage from Afghanistan.

Slim's unit at the Davis-Monthan Air Force Base, just outside of Tucson, Ariz., operated around the clock, flying Predator and Global Hawk drones thousands of miles away over Afghanistan, to monitor — and sometimes eliminate — "targets" across the war-ridden country. As a sensor operator for these remotely piloted aircraft, or RPAs, it was his job to coordinate the drones' onboard cameras, and, if a missile was released, to laser-guide the weapon to its destination.

These types of missions are part of the military's expanding drone program, which has developed a reputation for carrying out shadowy and highly classified operations — ones that sometimes blur legal or moral lines. As such, their use in warfare has been steeped in controversy. [How Unmanned Drone Aircraft Work (Infographic)]

Critics say firing weapons from behind a computer screen, while safely sitting thousands of miles away, could desensitize pilots to the act of killing. What separates this, they argue, from a battlefield video game?

But war is rarely so simple, and distance does nothing to numb the emotional impact of taking a life, said Slim (who is referred to here by his Air Force call sign in order to protect his identity).

"People think we're sitting here with joysticks playing a video game, but that's simply not true," Slim, who retired from the Air Force in 2011, told LiveScience. "These are real situations and real-life weapons systems. Once you launch a weapon, you can't hit a replay button to bring people back to life."

Killing machines?

In video games, players rarely make a human connection with the characters on their screen, but Predator drone operators often monitor their targets for weeks or months before ever firing a weapon, he added.

"While the enemy is the enemy, you still understand that they are a real person," Slim said. "To extinguish a person's life is a very personal thing. While physically we don't experience the five senses when we engage a target — unlike [how] an infantryman might — in my experience, the emotional impact on the operator is equal."

Still, the idea that being far away from the front lines could desensitize people to killing is not a new one. Arguably, the first weapon to give humans standoff distance in battle was the bow and arrow, said Missy Cummings, an associate professor of aeronautics and engineering systems at MIT in Cambridge, Mass., and director of the school's Humans and Automation Laboratory.

Cummings, who served as a naval officer from 1988 to 1999 and was one of the Navy's first female fighter pilots, said the argument that killing at a distance could desensitize soldiers has evolved in tandem with advances in war-fighting technology. The issue was similarly discussed when airplanes were introduced into warfare.

"You could make the argument that pilots haven't really been on the front lines since before World War II," Cummings said. "With some of the high-altitude bombing in World War II, pilots became pretty far removed from the actual combat." [Rise of the Drones: Photos of Unmanned Aircraft]

But drone pilots are sometimes thousands of miles away from the battlefield, and their physical distance takes on another dimension, since the entire operation is controlled across a network of computers rather than by soldiers on radios in the field. Yet, Cummings said the only difference is the location of the pilot and the amount of danger he or she may be in.

"Whether you're 5,000 miles away or 5 miles up, there aren't huge differences," Cummings told LiveScience. "When I flew F-18s, you saw everything through cameras and TV screens, just like how drone operators see today. I can't think of anybody now who releases a weapon purely on sight — you just don't do that anymore, because you have computer systems that do it for you."

The front lines of virtual combat

In fact, Nancy Cooke, a professor of cognitive science and engineering at Arizona State University's College of Technology and Innovation in Mesa, Ariz., argues drone pilots may be more emotionally impacted by killing at a distance because of how closely they have to monitor the situation before, during and after the attack. [After the Battle: 7 Health Problems Facing Veterans]

"The big difference is the level of detail that you can see on the ground," Cooke said. "When you operate a remotely piloted aircraft, even though you're there virtually, you have a lot of information about what's going on, on the ground."

Unlike pilots who physically fly into an area, release a weapon and sometimes never see the aftermath of their mission, drone operators regularly conduct lengthy surveillance following the strikes, exposing themselves to the often-grisly aftermath.

"While fighter pilots have to worry about being shot down, they rarely see the results of their attack," Slim said. "After an engagement, we have to conduct surveillance for quite a long time. Yes, we may only be seeing it, but sometimes, we're seeing it for hours on end, and that is part of the traumatic impact of the mission. It's a definite form of stress on the operator in and of itself."

In order to better understand how to screen pilots and their supporting units for mental health concerns, Wayne Chappelle, chief of aerospace psychology at the Air Force School of Aerospace Medicine at Wright-Patterson Air Force Base in Ohio, has conducted research on the potential psychological issues faced by drone operators. Most drone operators, Chappelle found, describe experiencing combat sensations that are remarkably similar to infantrymen on the front lines.

"They experience real and visceral reactions, like elevated heart rate and adrenaline — similar to what you would experience if you were in real combat, so they have that same heightened level of awareness and vigilance," Chappelle told LiveScience.

And despite conducting sometimes-lethal missions in front of a computer screen, Chappelle said drone operators have not shown any indication that they have become numb to the act of killing.

"[T]heir own personal lives aren't at risk, but the reality of what they're doing is really clear to them," he said. "I haven't seen or heard of anybody becoming desensitized, or having a nonemotional reaction, to the deployment of weapons."

But the battlefield — albeit virtual — is not the only place where drone operators experience tension.

Stressful situations

In 2011, Chappelle co-authored a study that identified areas of high stress within the Air Force's drone program. More than 1,400 members of the Air Force participated in the study, including 600 noncombatant airmen and 864 operators of Predator, Reaper and Global Hawk (unarmed) drones. [See Photos of NASA's Global Hawk Drones]

The individuals were asked to rank their level of stress on a scale from 0 to 10, with 10 representing feeling extremely stressed. Chappelle found that 46 percent of Reaper and Predator pilots reported "high operational stress."

From other questionnaires, Chappelle found that 17 percent of Predator or Reaper drone operators, and 25 percent of Global Hawk operators, show signs of what the Air Force terms "clinical distress," which includes depression, anxiety and other symptoms that interfere with job performance or disrupt family life. For comparison, approximately 28 percent of U.S. soldiers returning from Iraq are diagnosed with clinical distress, according to the Air Force.

In addition to the actual missions, the study found that some of the biggest factors contributing to stress were the long hours and frequent shift rotations required for drone operations. More than 1,300 drone pilots work for the Air Force, representing approximately 8 percent of all U.S. Air Force pilots, according to a recent report authored by Air Force Colonel Bradley Hoagland.

The Air Force currently supports 61 round-the-clock drone patrols in Afghanistan, Yemen and North Africa, but plans to expand to 65 patrols across the three regions by next year, Hoagland wrote in the report, which was released in August by the Brookings Institution, a nonprofit think tank based in Washington, D.C.

Doing more with less

Conducting patrols 24 hours a day, 365 days a year requires drone operators to work long shifts that sometimes last more than 10 hours at a time. This grueling schedule can take a toll, and Chappelle's 2011 study found that almost a third of active-duty drone operators reported symptoms of burnout.

Slim's unit in Arizona worked eight rotating shifts on a 24-hour period, and he said his team continuously felt pressure to keep up the operational pace in the face of ongoing budget constraints.

"We were doing so much more with so much less," Slim said. "For air crew, you have to have eight hours of uninterrupted sleep prior to starting a shift, but that's about the only regulation I know. This is a 24/7 job, and until we lower the operation tempo, we're always going to have this problem."

Chappelle said the Air Force implemented changes following his 2011 study, and took cues from other high-stress jobs that rely on shift work, such as police officers and hospital doctors. Some of the changes included adjusting schedules so that individuals could maintain proper circadian rhythms, which Slim said was something he struggled with as a sensor operator.

"Among RPA [remotely piloted aircraft] pilots, we found that a few years ago, their distress rates were around 28 percent," Chappelle said. "After folks had made some changes in the operational process to help them deal with fatigue, we were able to bring those stress rates down to 10 percent. And 10 percent is consistent with the general population."

But, Slim said he still witnessed high rates of burnout, which even caused some officers to leave the unit.

"The Air Force doesn't like to talk about it, but I have seen quite a bit of burnout and turnover," Slim said. "In Arizona, we went through almost a complete turnover in personnel since the unit started in 2006."

Combat stress and PTSD

Furthermore, the stress of working long hours occasionally carries over into drone operators' personal lives. Part of the problem is a lack of separation between work and home, Cooke explained.

"In traditional warfare, it's always been said that the social support you get from your unit is like a family," Cooke said. "In the drone world, it's a different way of doing warfare. Every day you're switching back and forth — you might be in a battle during the day, and then you go home to your family at night."

Researchers are unsure how this dynamic might affect drone operators in the long term, but Slim said balancing family life with the stress of his job caused tension in his household.

"The need to decompress is tremendous, but the problem is you can't talk about your work, what you have seen, or what you have done, because of security," Slim said. "Pretty soon, spouses don't understand why, and the friction really begins. In many ways, I wanted to tell my wife everything, but knew that I couldn't, so we mainly focused on how her day went. Needless to say, I didn't get a chance to decompress very much, and that led to a lot of pent-up stress."

Another area that will require more research is whether, and how, drone operators are affected by post-traumatic stress disorder (PTSD), which is characterized by nightmares, intrusive thoughts or avoidance of people or places. [The 10 Spookiest Sleep Disorders]

Based on the Air Force's health screenings, less than 4 percent of drone operators are at high risk of developing PTSD, Chappelle said. Roughly 12 to 14 percent of troops returning from Iraq and Afghanistan are at risk of developing PTSD, he added.

Still, studying PTSD in drone operators has been challenging, because a lot is still unknown about how traumatic stress affects regular troops, Cummings said.

"There's a debate about what PTSD looks like for drone pilots," she said. "One of the issues is we don't really understand how much PTSD is happening in regular pilots. We can't even make assessments about whether drones cause more or less PTSD, because we don't have a basis for comparison."

And with the military looking to expand drone operations, it may be premature to disregard the potential impact of PTSD.

"This is going to be an increasingly prevalent way of doing warfare, and there's an attitude among military people that because you're not in harm's way, you're not going to have stress-related problems," Cooke said. "PTSD is a big problem, and I think it may actually be intensified [with drone warfare]. We're trying to get these numbers and understand these details now, because it's been my feeling for a while that this could blindside us."

Follow Denise Chow on Twitter @denisechow. Follow LiveScience @livescience, Facebook  Google+. Original article on LiveScience.