WASHINGTON – On May 9, 1967, Sigmund and Agnes Tycz of Milwaukee received a letter from their 22-year-old son, Marine Sergeant James Neil Tycz, who marveled at his new “Sarge’s growwwl.”

“Would you believe [with] my squeak??!” he wrote, a reference to his high-pitched voice.

The next day, Tycz and three other American servicemen were killed on Hill 665 near Khe Sanh, Vietnam, close to the Laos border, in a battle with North Vietnamese troops. It was too dangerous to recover their bodies, so for decades, they were listed as “killed in action – body not recovered.”

But this year, the military informed the families that it had finally identified the remains. On Tuesday, the 38th anniversary of their deaths, three of the men will buried at Arlington National Cemetery. A fourth man was buried last month, but will be honored at the ceremony.

Tycz, who was posthumously awarded the Navy Cross for extraordinary heroism, led a seven-man reconnaissance team into enemy territory, where members came under fire from a North Vietnamese Army unit of between 30 and 50 men.

Tycz was just 5 feet 9 inches tall and 125 pounds when he joined the military, recalled his older brother, Phillip Dale Tycz. “He had a high voice,” said Mr. Tycz, who now lives in Plano, Texas. “It was hard for us at home to picture him as a sergeant. In movies, these are big guys. He wasn’t a take-charge-type kid. He was very humble.”

The Navy Cross citation says that when a hand grenade landed near one of the seriously wounded Marines, Tycz “courageously and with complete disregard for his own personal safety moved forward, picked up the grenade and attempted to throw it back at the enemy.”

But the grenade exploded after going just a short distance, critically wounding Tycz.

The family of another serviceman from that group, 20-year-old Navy corpsman Malcolm Miller of Tampa, Fla., went through a similar emotional journey.

“We held out hope for a long time,” said Miller’s older sister, Sandy Keheley of Madison,Ga. “My father kept writing letters trying to get confirmation. In the’80s, we finally decided it had really happened. We had to accept it.”

In Miller’s last letter to the family, he complained, “Don’t y’all love me anymore? I haven’t received any mail from any of you.” The family had been writing, Ms. Keheley said, but Miller was in the backcountry, where mail had not gotten through.

The sister of another missing serviceman, Marine Second Lieutenant Heinz Ahlmeyer Jr., was stunned when the military informed her that it had identified his remains.

“I did not expect them ever at this point to find it,” said Irene Healea, who lives in Watertown, Tenn. “If he had been killed, and the body hadn’t been recovered, we’re looking at a place where there are scavenger animals. Would you really expect them to find what was left?”

Ahlmeyer, who was 23 when he died, grew up in Pearl River, N.Y., about 30 miles north of New York City, and played soccer at the State University at New Paltz. An award in his name is given annually at the school.

The fourth serviceman, Marine Lance Corporal Samuel Sharp Jr., of San Jose, Calif., was buried in his hometown last month.

“It’s been hard, like there’s still something missing,” said a sister, Janet Caldera, of Spokane, Wash. “Until you have him come back, you still wonder if he was really killed. You have that question in the back of your head. We never thought we’d have the remains come back. It’s kind of a miracle to us.”