President Joe Biden will award the Medal of Honor, the nation’s highest recognition for combat valor, to four U.S. Army veterans who fought their way through hellacious battles during the Vietnam War more than 50 years ago, White House officials said Monday.

The recipients are Spc. 5 Dwight Birdwell, who led an armored unit through a bloody ambush in 1968; Maj. John Duffy, a Special Forces officer who fought off an attack on his fire base in 1972; Spc. 5 Dennis Fujii, who directed airstrikes on advancing forces while under fire in Laos in 1971 and after surviving a helicopter crash; and Staff Sgt. Edward Kaneshiro, who single-handedly cleared a trench of enemy fighters using grenades and a rifle in 1967.

All four will have previous awards upgraded, with Kaneshiro receiving the honor posthumously. The ceremony is scheduled for July 5.

Birdwell, 74, said in a phone interview Monday that he received notification of his award from Biden last month and that the president told him twice it was a “big deal.”

He previously received the Silver Star, the U.S. military’s third-highest award for combat valor, for his actions on Jan. 31, 1968. Others in his unit had sought the upgrade for years.

“Frankly,” he said, “it’s a bit overwhelming.”

Birdwell was assigned to a cavalry unit with the 25th Infantry Division when a major military installation, Tan Son Nhut Air Base, came under attack. North Vietnamese soldiers and Viet Cong guerrillas had just launched the Tet Offensive, marked by surprise attacks across Vietnam on South Vietnamese soldiers, U.S. troops and their allies. Birdwell and his fellow soldiers were ambushed while driving to the air base to assist, and Birdwell’s tank commander was incapacitated with gunfire.

“Specialist Birdwell immediately took command of the vehicle and began placing effective suppressive fire on the enemy force until all of his ammunition was expended,” according to his Silver Star citation. “He then retrieved an M-60 machine gun and continued to place devastating fire on the enemy until his weapon became inoperable.”

Birdwell, “with complete disregard for his own safety,” then ran under enemy gunfire to get ammunition from other damaged vehicles, distributed it to fellow soldiers and helped evacuate the wounded. He was wounded in the torso and face during the battle.

Birdwell said Monday that he still replays “just about daily” what happened during the battle, and whether there is anything he could have done better.

“I also think quite a bit about the bullets whizzing by me,” he said. “I can still hear that unique sound they make. It’s a bit terrifying. It stays with you.”

Duffy previously received the Distinguished Service Cross, the Army’s second-highest award for valor in combat, for his actions April 14 and 15, 1972, when his base came under attack. He braved enemy fire to coordinate airstrikes on enemy antiaircraft guns, scrambled about his base to treat wounded Vietnamese soldiers and requested U.S. aircraft launch gun runs on his position after enemy forces advanced within 10 meters, according to his award citation. He now lives in Santa Cruz, Calif., the White House said.

Fujii previously received the Distinguished Service Cross for his role in rescue operations in Laos and Vietnam between Feb. 18 and 22, 1971, after his unit’s medical evacuation helicopter came under fire and crashed. He waved off rescue from another helicopter and stayed on the battlefield, administering aid to other soldiers.

The following night, Fujii called in American helicopters to repel another enemy attack. Over the following 17 hours, he braved enemy fire repeatedly, leaving a trench to observe enemy positions and direct airstrikes on them. He now lives in Hawaii, the White House said.

Kaneshiro was an infantry squad leader with the 1st Cavalry Division on Dec. 1, 1966, when his unit was attacked by North Vietnamese soldiers. He fought them off and allowed the withdrawal of his platoon. He was killed March 6, 1967, during another operation in Vietnam.