Donald Ballard was 20 years old, married, and working in a dental lab with the hope of someday becoming a dentist when he decided to join the Navy in 1965. Midway through basic training, informed that dental assistants were plentiful but corpsmen were in short supply, he was sent to surgical assistant school. He assisted in orthopedic and general operations, then was "volunteered" to serve as a medic with the Marine Corps. His unit soon sailed for the Mediterranean, where it made a simulated amphibious landing on Corsica. While there, Ballard and the other American servicemen got to know some French Legionnaires, who told them daunting stories about Vietnam. In 1967, he was sent into the war zone on a transport plane, which had a strange smell. He later found out that it served as a "morgue plane" on its outbound trips.

On the day he arrived, he was issued a .45-caliber pistol, but there was no magazine. "Don't worry, Doc," the supply sergeant told him when he was asked about it. "If you need a weapon, there'll be plenty on the ground when the fighting starts." He would learn from the personal observation that corpsmen were more likely to be wounded than riflemen because they had to be the first men standing after everyone else had hit the dirt. "Corpsmen up!" was part of the Marine battle cry.

Ballard was shot in one of his Marine unit's first actions and received the first of his three Purple Hearts. (He should have had eight by the time left Vietnam, but he tended to his own wounds on five occasions.)

On May 16, 1968, having just treated two Marines for heat exhaustion during a patrol, Ballard was returning from the evacuation landing zone when his company was ambushed by a North Vietnamese unit firing automatic weapons and mortars. He rushed to a group of wounded Marines, one of whom had both legs shredded by a grenade. As he kneeled to care of him, another Marine who had been shot in the face yelled, "Grenade!" Ballard's first thought as he saw it hit nearby was that it would kill the men he was treating if it exploded, so he threw himself on the grenade and cradled it to his body. After what seemed like an eternity with no explosions, he threw the grenade away and turned his attention back to the wounded men. He was told later that the grenade, which apparently had a defective fuse, had exploded in the air.

After being wounded again in the fall of 1968, Ballard returned to the United States and was assigned to work in a Navy surgical clinic. One day an Army recruiter came to the hospital and offered him a commission to make a "lateral transfer" from the Navy. He had already decided to make a career of the military, so he joined the Army. While waiting to attend Officer Candidate School, he was informed that he was to receive the Medal of Honor. It was presented to him on May 14, 1970, by President Richard Nixon, who told him, "the country has a lot to be thankful for, having men of your caliber. I am very proud of you."

After serving a total of 35 years active and reserve, Donald Ballard retired from the Kansas National Guard in 2000 as a colonel.