(CNN) -- The pilot glanced outside his cockpit and froze. He blinked hard and looked again, hoping it was just a mirage. But his co-pilot stared at the same horrible vision.
"My God, this is a nightmare," the co-pilot said.
"He's going to destroy us," the pilot agreed.
The men were looking at a gray German Messerschmitt fighter hovering just three feet off their wingtip. It was five days before Christmas 1943, and the fighter had closed in on their crippled American B-17 bomber for the kill.
The B-17 pilot, Charles Brown, was a 21-year-old West Virginia farm boy on his first combat mission. His bomber had been shot to pieces by swarming fighters, and his plane was alone in the skies above Germany. Half his crew was wounded, and the tail gunner was dead, his blood frozen in icicles over the machine guns.
But when Brown and his co-pilot, Spencer "Pinky" Luke, looked at the fighter pilot again, something odd happened. The German didn't pull the trigger. He nodded at Brown instead. What happened next was one of the most remarkable acts of chivalry recorded during World War II. Years later, Brown would track down his would-be executioner for a reunion that reduced both men to tears.
Listen: A bond between enemies
Living by the code
People love to hear war stories about great generals or crack troops such as Seal Team 6, the Navy unit that killed Osama bin Laden. But there is another side of war that's seldom explored: Why do some soldiers risk their lives to save their enemies and, in some cases, develop a deep bond with them that outlives war?
And are such acts of chivalry obsolete in an age of drone strikes and terrorism?
Charles Brown was on his first combat mission during World War II when he met an enemy unlike any other.
Those are the kinds of questions Brown's story raises. His encounter with the German fighter pilot is beautifully told in a New York Times best-selling book, "A Higher Call." The book explains how that aerial encounter reverberated in both men's lives for more than 50 years.
"The war left them in turmoil," says Adam Makos, who wrote the book with Larry Alexander. "When they found each other, they found peace."
Their story is extraordinary, but it's not unique. Union and Confederate troops risked their lives to aid one another during the Civil War. British and German troops gathered for post-war reunions; some even vacationed together after World War II. One renowned American general traveled back to Vietnam to meet the man who almost wiped out his battalion, and the two men hugged and prayed together.
What is this bond that surfaces between enemies during and after battle?
It's called the warrior's code, say soldiers and military scholars. It's shaped cultures as diverse as the Vikings, the Samurai, the Romans and Native Americans, says Shannon E. French, author of "Code of the Warrior."
The code is designed to protect the victor, as well as the vanquished, French says.
"People think of the rules of war primarily as a way to protect innocent civilians from being victims of atrocities," she says. "In a much more profound sense, the rules are there to protect the people doing the actual fighting."
The code is designed to prevent soldiers from becoming monsters. Butchering civilians, torturing prisoners, desecrating the enemies' bodies -- are all battlefield behaviors that erode a soldier's humanity, French says.
The code is ancient as civilization itself. In Homer's epic poem, "The Iliad," the Greek hero Achilles breaks the code when his thirst for vengeance leads him to desecrate the body of his slain foe, the Trojan hero Hector.
He's going to destroy us!
Charles Brown, B-17 bomber pilot
Most warrior cultures share one belief, French says:
"There is something worse than death, and one of those things is to completely lose your humanity."
The code is still needed today, French says.
Thousands of U.S. soldiers returning from wars in Iraq and Afghanistan are struggling with post-traumatic stress disorder. Some have seen, and have done, things that are unfathomable.
A study of Vietnam veterans showed that those who felt as if they had participated in dishonorable behavior during the war or saw the Vietnamese as subhuman experienced more post-traumatic stress disorder, French says.
Drone warfare represents a new threat to soldiers' humanity, French says.
The Pentagon recently announced it would award a new Distinguished Warfare Medal to soldiers who operate drones and launch cyberattacks. The medal would rank above the Bronze Star and Purple Heart, two medals earned in combat.
At least 17,000 people have signed an online petition protesting the medal. The petition says awarding medals to soldiers who wage war via remote control was an "injustice" to those who risked their lives in combat.
Outgoing Defense Secretary Leon Panetta defended the new medal at a February news conference.
"I've seen firsthand how modern tools, like remotely piloted platforms and cybersystems, have changed the way wars are fought," Panetta says. "And they've given our men and women the ability to engage the enemy and change the course of battle, even from afar."
Still, critics ask, is there any honor in killing an enemy by remote control?