An 83-year-old retired Marine kept a promise he made to a fellow officer while they were hunkered down in a bunker during the Vietnam War.

Retired Marine Master Sgt. William H. Cox and Retired Marine First Sgt. James 'Hollie' Hollingsworth were shielding themselves from rockets and mortars in 1968 as they were fighting in the Marble Mountains during the war on New Year's Eve.

The two men, who were strangers to each other, had decided if they made it out of the bunker and survived the war, they would contact each other every New Year's Eve.

For the next five decades they kept that promise - every New Year's Eve they would catch up.

Earlier this year, Cox traveled from Piedmont, South Carolina, to see Hollingsworth, 80, in Hephzibah, Georgia.

The 83-year-old made the trip so that he could say goodbye to his dear friend who was dying.

Honor: Retired Marine Master Sgt. William H. Cox (left) kept his promise to stand guard at his friend's funeral, Retired Marine First Sgt. James 'Hollie' Hollingsworth on October 24

For decades, Cox (left) spoke to Hollingsworth (right) on New Year's Eve after they became close friends when they survived a 1968 NYE attack during the war. In July (above), Hollingsworth asked Cox to give the eulogy and stand guard at his funeral

The two men flew over 200 combat missions together, which resulted in Cox (left) to consider Hollingsworth (right) to be a 'brother'. The two men served in the Marine helicopter squadron VMO-2. Obviously, Cox agreed to honor his dear friend

While visiting, Hollingsworth asked his buddy to make him one last promise.

He asked him to stand guard over his casket and deliver the eulogy at his funeral, to which Cox accepted.

'I said, "Boy, that's a rough mission you're assigning me to there,"' Cox told Greenvilleonline.com.

A photo shared to Facebook by Hollingsworth's son shows the two men catching up like old times in deep conversation back in July.

'Two great Marines were reunited once again. These two flew over 200 missions on the same Huey in Vietnam,' his son wrote alongside the image.

'I have always been proud of my father and his service to our Country. Love hearing the stories from his closest friend.'

His son said the last thing Cox told Hollingsworth was a phrase they often exchanged when they closed their conversations - 'Hollie, you keep 'em flying, and I'll keep 'em firing.'

Cox, who served in the Marine helicopter squadron VMO-2 with Hollingsworth, made sure to keep his final promise when the time came months later.

The 83-year-old put on his dress blues and stood guard over his friend's casket during his funeral service on October 20.

He also delivered a heartfelt eulogy for Hollingsworth - whom he flew over 200 combat missions with during their time in the Marines.

When he closed the eulogy at his funeral last month, Cox (above in 2011) repeated a phrase he would tell his friend during their missions and when he would say goodbye to him on the phone: 'Hollie, you keep 'em flying, and I'll keep 'em firing.'

Closing the emotional eulogy, Cox repeated: 'Hollie, you keep 'em flying, and I'll keep 'em firing.'

A photo taken of Cox standing next to Hollingsworth casket was shared to Facebook by his son, Bill Cox.

'My 83 year old father, Master Sergeant William H.Cox, USMC, Retired, honoring one of his Vietnam brothers, First Sergeant James J. Hollingsworth (Hollie),' he captioned it.

'They made a pact to stay in touch, if they survived their tour, and they did. Both were door gunners, and dad was the only enlisted man in VMO-2 to be awarded the DFC in Vietnam.

'He has to use a cane most of the time now, but he insisted on not using it during his vigil at the casket and at the funeral.'

Since sharing the photo on November 5, the emotional photo has been shared thousands of times with many fellow Marines saluting the pair for their service.

Cox said that his bond with Hollingsworth as a Marine was 'different from any other branch of service' and that he considered him to be 'a brother.'