As the two Marines hunkered down, they made a pact: “If we survived this attack or survived Vietnam, we would contact each other every year on New Year’s,” Cox said.

For nearly five decades, Cox, who lives in Piedmont, S.C., and Hollingsworth of Hephzibah, Ga., kept their promise.

And earlier this year, Cox kept another promise: He stood guard at Hollingsworth’s casket and then delivered the eulogy at his funeral.