"Keep breathing," Campbell told himself, repeating a recurring line from DiCaprio's "The Revenant."
The mantra was a small thing Campbell could do for himself while he awaited a medical evacuation Jan. 16 after an attack in eastern Afghanistan's Paktika province. It kept him going until he fell unconscious, he later wrote in a message to friends and family.
Campbell and a teammate from Joint Base Lewis-McChord's 2nd Battalion, 75th Ranger Regiment now are recovering at Walter Reed Military Medical Center.
Campbell, 22, was the more seriously wounded of the two, with a bullet lodged close to his heart. Three other bullets passed through his body.
His lung nearly collapsed at the scene of the attack. The litter meant to help lift him off the ground broke. Later, his heart stopped on one of his medical flights.
Now, "he's doing very well," said his mother, Carol Campbell of Kansas City. She traveled to an Army hospital in Germany to spend time with him before his transfer to Walter Reed.
"Mentally, he's fine," she said. "He's able to interact. He's able to stand up and walk and do physical therapy, which is a miracle."
Campbell was hit on a mission linking his Ranger team with Afghan special operations soldiers. They were attacked with small arms and with something that exploded, causing shrapnel to splinter in a compound they visited, according to the Ranger battalion.
Campbell also was hurt around his eyes, where shrapnel struck, his mother said.
He serves in a unit that has been deploying to Afghanistan more or less continuously since the terrorist attacks on the World Trade Center and the Pentagon in 2001.
"We have remained in contact with the enemy in either Iraq and/or Afghanistan since 2001," battalion Commander Lt. Col. Jay Bartholomees said at a September ceremony recognizing his soldiers' recent contributions in Afghanistan.
The Ranger battalion's ongoing assignments there are a reflection of a persistent Taliban insurgency against the Afghan government. About 9,800 American military service members are in Afghanistan now, down from a peak of more than 100,000 in 2011.
Special Operations units, such as the Rangers and Green Berets, reportedly are still on the front lines closely supporting Afghan forces. Staff Sgt. Matthew McClintock, a Green Beret from the Washington National Guard, was killed in a battle in southern Afghanistan's Helmand province earlier this month.
Campbell joined the battalion a little more than two years ago and has deployed to Afghanistan several times, his mother said. He joined the Army immediately after high school in Southern California and plotted a course that would make him an Army Airborne Ranger, she said.
"I can't even explain how proud I am of my young man," she said.
In his letter to friends and family, Campbell thanked his teammates for keeping him alive after the attack. He praised the flight surgeons who revived him when his heart stops and the nurses who've tended to him.
"I owe a lot of people thank-yous for everything that has happened in the past week," he wrote.
He also gave thanks to DiCaprio.
"Believe it or not, when I was laying there all jacked up, the movie 'The Revenant' came to mind," he wrote. "All I could think of was that line, 'Keep breathing.' "