Decades earlier, the father had also risked everything to serve his country and had come away with a permanent physical wound and a deep distaste for what soldiers are asked to do. But he let his son make his own decisions.
The attacks by the North Vietnamese and Viet Cong had deflated optimistic U.S. assessments of the war's progress and began to turn American public opinion against the war.
By January 1970, Murphy was at war and on a mountaintop of his own, Nui Ba Den, a 3,235-foot dormant volcano that looms above a wide plane northwest of Saigon.
Throughout years of intense fighting, American troops held just a few acres at the mountain's peak, with the Viet Cong owning the rest. The two forces fought regular battles to try to drive the other away.
The mountain's caves were storehouses for insurgent supplies arriving from North Vietnam via the Ho Chi Minh Trail in Cambodia, 18 miles away. From the mountain, the Viet Cong could spot approaching American troops before they arrived and direct shelling onto the camp where Murphy was stationed in the nearby provincial capital of Tay Ninh City.
"They hit us so often we used to call it 'Rocket City,' " Murphy recalled.
On Jan. 4, 1970, as they had every few months since 1965, U.S. forces again hurled themselves at the mountain, hoping finally to take it. Shortly after dawn three days later, Murphy - firing his rifle from behind a rock - was lifted high into the air when a grenade exploded. It fractured his ankle and pierced his legs with shrapnel from his hips to his feet.
"I remember as clear as a bell floating down and saying, 'I'm dead. What are my parents going to think?' " recalled Murphy, who to this day is prevented by pain from carrying his briefcase in his left hand.
A month after he was injured, Murphy's best Army buddy - a 20-year-old radio operator from Bay Shore named Tommy Wynne - was killed in combat. Also killed was the medic who pulled Murphy to safety, whom everyone called "Gushy."
U.S. forces never took the mountain, and, in 1973, ground forces abandoned the country altogether. It was in that place and time, that Daniel Murphy's view of the soldiers' life was formed.
"It wasn't a matter of political belief, but Vietnam left a bad taste in my mouth that soldiers were used as cannon fodder," said Murphy, the National Judge Advocate for the Military Order of the Purple Heart, an advocacy group for wounded veterans.
The father had rarely spoken of Vietnam while Michael was growing up, not wanting to share the horror - or plant a career idea - with a young, impressionable son. So that night in the car, Murphy offered some words of caution.
"I said, 'Michael, you know my disenchantment with the military after being in Vietnam,' " Murphy recalled. " 'I thought you wanted to go to law school?' "