In 1967, Patrick Gallagher, just 23 years old, was murdered in an ambush in Danang, Vietnam.
In commemoration of him, the USS Patrick Gallagher will be the new name of a US Navy warship.
Although tomorrow will be a "fun day for us as a family," according to his sister Pauline, they are still in grief for Patrick.
Speaking to RTÉ's Morning Ireland, she said that her brother had moved to the US in 1962 and was enrolled in law school at the time the Vietnam War intensified.
On March 13, 1967, she claimed, he was murdered on his "very last day" in Vietnam. Three days earlier, she added, he had saved his friends' lives when grenades were hurled into the bunker they were resting in.
"He threw the first two grenades out of the bunker but the third landed between two of his comrades," she said.
"He called for the others to get out, and they obeyed, throwing himself on that grenade to absorb the blast. He picked up the grenade and hurled it into a lake nearby, where it detonated without causing any harm to anyone.
"For that, he received the navy's highest medal."
According to Ms. Gallagher, US Senator Chuck Schumer is in favour of a petition to rename a ship in Patrick's honour.
"Tomorrow is a very exciting day for us as a family but we still have the loss of our brother, who we miss dearly," Mrs. Gallagher stated.
"The ship is a great honour but at the same time the grief still remains."