For some veterans of war, recovering from trauma means going back to the battlefield.

The battlefield isn’t real, however, nor are the gunfire and soldiers. But the scene is as a veteran like Chris Merkle remembers it. Behind a pair of virtual reality goggles, Mr. Merkle is once again invading Iraq on one of his longest days. Gunfire erupts, and he sees Iraqi men go down, not knowing whether he shot them or someone else did. He has no time to question, he is on the move. In his mind, he is back at war.

When Mr. Merkle removes his goggles, he is back at the Veterans Affairs Healthcare System in Long Beach, Calif. The clinic is one of dozens of centers in the U.S. using virtual-reality exposure therapy, an increasingly popular treatment method for mental-health conditions such as post-traumatic stress disorder, phobias and anxiety.

Mr. Merkle, 41, began using the therapy in the winter of 2013 after multiple tours in Iraq and Afghanistan left him numb and angry, suffering from what the doctors told him was PTSD. He has completed treatment and exhibits few symptoms, but returns periodically for follow-up sessions.

“I was angry, I was stressed. I tried a lot of things, but when I tried virtual reality it was like a toxic release,” said Mr. Merkle, who now works for the Long Beach VA facility in veteran outreach. “You’re not just talking to a therapist on a couch,” he said. “You’re in that event, you’re reliving those moments.”

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