From the start of American operations in the Vietnam War in 1961  to to the end of direct U.S. military involvement in 1973, more than 3 million Americans served in the conflict, half of whom saw combat. The deeply divisive war came to define a generation, as did its toll on human life.

During the Vietnam War, 303,644 Americans were wounded and 58,307 killed. While nearly 7,500 women served in Vietnam, the majority of whom were nurses, the overwhelming majority of combat injuries and deaths were men — though not all.

That means that for each casualty, there was one less husband, friend, brother, father, or son; in a few cases, families were forced to endure multiple tragedies.

Here are three fathers and their sons who made the ultimate sacrifice for their country during Vietnam.

Richard B. Fitzgibbon Jr. and his son Richard B. Fitzgibbon III

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Richard Fitzgibbon Jr., left, and his son Richard Fitzgibbon III, right.

Tech. Sgt. Richard B. Fitzgibbon Jr., a former Navy veteran who served during World War II and then later joined the Air Force, was the first American killed in the Vietnam War. Fitzgibbon was shot by a fellow airman who had been drinking heavily following an argument between the two, according to a 2012 report. Fitzgibbon was handing out candy to a group of children in Saigon when the man walked over, drew his sidearm, and shot him. He died of his wounds days later on June 8, 1956. He was 36 years old.

His son, Lance Cpl. Richard B. Fitzgibbon III, was killed in combat on Sept. 7, 1965, in Quang Tin, Vietnam, at the age of 21. His aunt, Alice DelRossi said that Fitzgibbon followed in his father’s footsteps, joining the Marines after graduating high school, because he wanted to connect to the place where his father had died.

However, it wasn’t until 1999 that the elder Fitzgibbon found his rightful place on the Vietnam Memorial wall. When the Department of Defense began compiling its casualty database for the war, the conflict’s start date was listed Jan. 1, 1961, five years after his death.

With the help of U.S. Rep. Ed Markey of Massachusetts, the Fitzgibbon family succeeded in persuading DoD to recognize that military advisers were in Vietnam as of Nov. 1, 1955, which made Fitzgibbon Jr. the first American casualty of the war.

Leo Hester Sr. and his son Leo Hester Jr.

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Leo Hester Sr., left, and his son Leo Hester Jr., right.

On March 10, 1967, Navy pilot Lt. Cmdr. Leo Claude Hester Sr. died in an aircraft crash in Ninh Thuan, Vietnam. He was 43 years old. Tragically, less than two years later his son, an aviator in the Army, would suffer the same fate.

Twenty-year-old Army Warrant Officer Leo Claude Hester Jr. was also killed in an aircraft crash, on Nov. 2, 1969, while serving as a helicopter pilot in Tay Ninh, Vietnam.

According to the website, both father and son are buried next to each other at Barrancas National Cemetery in Pensacola, Florida.

Fred C. Jenkins and his son Bert M. Jenkins

Army Spc. 5 Fred C. Jenkins, a welder in the Ordnance Corps, drowned on April 2, 1968, in Hau Nghia, Vietnam, at the age of 49. A year later, his son, Warrant Officer Bert McCree Jenkins was killed in action on April 28, 1969, after the Huey he was piloting was shot down by small arms fire. Jenkins, who served with the Army’s 1st Aviation Brigade, 1st Infantry Division, was flying armed reconnaissances in support of a convoy. He was hit during the engagement and succumbed to his wounds in a hospital after he was recovered.

Bert Jenkins was 29 years old when he was killed and is buried at the Louisville Memorial Gardens in Kentucky.