The percentage of soldiers who reported killing an enemy combatant rose from 33 percent to 48 percent from 2009 to 2010 according to a survey by a mental health advisory team.

In addition, 62 percent of soldiers and almost 67 percent of Marines reported surviving a blast of an improvised explosive device, and more than 70 percent of both soldiers and Marines reported that a member of their unit had been killed in combat.

"Mostly what's reflected in the data [are] the incredibly high rates of combat," says Col. Paul Bliese, PhD, of the Center for Military Psychiatry and Neuroscience at the Walter Reed Army Institute of Research. He led the survey team of Army, Navy and Air Force psychologists, researchers and behavioral health technicians to Afghanistan in July 2010.

This combat exposure has dampened morale and increased feelings of acute stress, says Bliese.

The team surveyed 1,246 soldiers and Marines drawn from randomly selected combat platoons. They found that 17 percent of soldiers reported acute stress last year, compared with 13 percent in 2009. In addition, the survey found that just over 15 percent of soldiers on their third or fourth deployment said they took medication for a mental health condition compared with less than 5 percent of soldiers on their first deployment.

The percentage of Marines who reported acute stress, depression or anxiety was just under 19 percent — more than twice the percentage of a similar sample from Iraq in 2007. Unit morale was also a problem, with only 12 percent of Marines reporting high or very high morale compared with 23 percent from a 2007 Iraq survey.

Now that the survey is complete, Bliese wants to follow up with units that experienced a lot of combat since prior research suggests that those who directly witness and participate in such violent experiences are more likely to have psychological problems three to six months after returning home, he says.

"We want to make sure they're given the best of the best when they come back. It's not a trivial matter," Bliese says.

—C. Munsey