This month marks the 60th anniversary of the outbreak of the Korean War, a three-year conflict that claimed 4 million lives, 36,000 of them American. It’s been dubbed “The Forgotten War” — US military historians focus more on Vietnam, World War II and even the Civil War. But one battle will never be forgotten: The Chosin Reservoir Campaign.

In the winter of 1950, the 12,000 Marines and 3,000 soldiers of the 1st Marine Division were surrounded by 120,000 Chinese soldiers at the Chosin Reservoir. Trapped 78 miles behind enemy lines and battered by sub-zero temperatures, the American troops fought their way out, taking their dead and wounded with them.

As the men reached the coastline, 98,000 civilians followed them, desperate to escape Communist rule in North Korea. The Marines, soldiers and sailors volunteered to stay for three more days, under fire, until all of the refugees were loaded onto ships and brought safely to South Korea.

Seventeen Medals of Honor, 73 Navy Crosses and 23 Distinguished Service Crosses were awarded, making Chosin one of the most decorated battles in American history.

The Chosin Reservoir Campaign is taught, along with Belleau Wood and Iwo Jima, to every Marine recruit and officer candidate to illustrate the standard set by those who have gone before. Whether we’re on patrol in Afghanistan, providing humanitarian aid in Haiti or just cleaning the barracks at Camp Pendleton, we have a legacy to uphold by completing our mission, no matter what challenges we face. Marines get the job done. Period.

But when I set out to make the first-ever documentary about Chosin with Marine Capt. Brian Iglesias (after we’d both left active duty), we discovered that not even the Marine Corps had archived first-person accounts of the battle on film. We took an oral-history approach to the project and spent eight months on the road collecting stories from 185 Korean War veterans in 27 cities across the United States. As fellow combat veterans, we forged a unique connection with the men we interviewed.

Time and time again, these men told us stories that they had never told anyone — not their wives, their children or their closest friends.

Brothers Juan and Jesse both fought at Chosin in the 7th Marines. After the war, they came home and raised their families in the same San Antonio neighborhood, but never spoke to each other about Korea.

The day we met, one brother described the first time he killed a man, first thrilled and then saddened as he realized the enemy soldier was a teenager, just like him. The other recalled fighting through an overwhelming night attack, his platoon of 40 Marines reduced to seven men by morning. There were tears, laughter and even wonder at their ability to remember events they hadn’t spoken of in six decades.

For them, as for many combat vets, these things felt best left on the battlefield. How can you describe losing friends, feeling absolute terror or taking another man’s life without the worry of alienating a loved one?

Those who serve are also a humble bunch, and it feels awkward to explain your own triumphs. So, you come home and try to move on.

There were two lessons learned on this journey. The first: Find a mission. The military gives you a higher sense of purpose that is difficult to find anywhere else. These men adjusted by going to school, raising families, starting businesses and volunteering. They kept themselves busy.

The second lesson: Don’t carry the weight of your experiences alone. Despite the pain relived during the interviews, every man shook our hands afterward and smiled and joked with us, more light-hearted.

They asked about our experiences in Iraq, and two generations of warriors realized that they were, at their core, the same American kids who have always stepped forward and answered the call. These men allowed us to shed the weight of our war.

Anton Sattler is a captain in the Marine Reserves and the producer of “Chosin” (frozenchosin.com). “Chosin” premieres in New York at Symphony Space at 6:30 pm Wednesday.