The USS Fitzgerald collided with a Philippine-flagged merchant vessel about 56 miles off the coast of Japan on Saturday.
Seven sailors were later found dead in flooded compartments on the ship.
When the Fitzgerald collided with the merchant ship, 37-year-old Fire Controlman 1st Class Gary Leo Rehm Jr., "leapt into action," according to The Daily Beast.
The Fitzgerald was struck below the waterline, and Rehm Jr.'s family was told by the Navy that he went under and saved at least 20 sailors, according to WBNS-10TV in Columbus, Ohio.
But when he went back down to get the other six sailors, the ship began to take on too much water, and the hatch was closed, WBNS-10TV said.
"That was Gary to a T," Rehm Jr.'s friend Christopher Garguilo, told NBC4i in Columbus, Ohio. "He never thought about himself."
"He called [the sailors on the ship] his kids," his uncle, Stanley Rehm Jr., told The Daily Beast. "He said, 'If my kids die, I'm going to die.'"
Rehm Jr. was known to invite "his kids" over to his house in Virginia when their ship was docked in the US, his uncle said. "He was always ready to help anybody who needed it. He was just that kind of guy."
"Gary was one of those guys that always had a smile on his face," Daniel Kahle, who had served with Rehm Jr. on the USS Ponce, told The Chronicle-Telegram. "(Gary was) such a great guy and (it's) such a great loss. He needs to be remembered for the person we all knew him to be."
Rehm Jr.'s uncle told The Daily Beast that he followed in the footsteps of his grandfather by joining the Navy straight out of high school.
Rehm Jr. was considering retiring soon but also hoped to make captain one day, his uncle told The Daily Beast.
The Fitzgerald is named after another sailor, Navy Lt. William Fitzgerald, who, like his father, also joined the Navy right out of high school.
In August 1967, he was advising South Vietnamese forces at a compound near the Tra Khuc River delta when they came under heavy Vietcong fire.
Fitzgerald ordered the South Vietnamese forces and civilians to escape into the river on small boats, but he was killed while covering their escape with small-arms fire.
Rehm Jr. was raised in Elyria, Ohio, and is survived by his wife, Erin.
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