On November 16, 1968, Major Colin Luther Powell was serving his second tour of duty in Vietnam, this time as the assistant Chief of Staff to the commander of the U.S. Army’s 23rd Infantry Division (also called the Americal Division). It was mostly a desk job, but that day Powell was traveling by helicopter with his commanding officer, Major General Charles M. Gettys, to inspect a captured North Vietnamese camp when their chopper clipped a tree during landing and crashed.

Powell broke his ankle in the violent crash, but the injury didn’t prevent him from rushing back into the wreckage again and again to save the lives of Gettys, his chief of staff and one of the pilots. At one point, Powell tore away parts of the flaming wreckage with his bare hands to free a trapped comrade, knowing that the wrecked chopper could explode at any second.

Powell received the Soldier’s Medal for his bravery that day, which added to the Bronze Star and Purple Heart that he also earned during his two tours in Vietnam.

Decades later, Colin Powell would become America’s first Black national security advisor, the nation’s youngest chair of the Joint Chiefs of Staff and the first Black Secretary of State. During the Persian Gulf War of 1991, Powell resolved not to repeat the costly mistakes of America’s failed war in Vietnam and executed an overwhelming show of force now known as the Powell Doctrine.

The qualities that later made Powell such an effective military advisor first “blossomed” during his Vietnam service, says Jeffrey J. Matthews, a professor of business and leadership at University of Puget Sound and author of the biography Colin Powell: Imperfect Patriot.

“Powell’s commanders commented consistently about his extreme dedication, his hard work, his commitment, and his competence as both an officer in the field and as a member of a staff,” says Matthews. “If you want to understand Powell’s ultimate prominence, it was because he used those qualities to become a great supporter, subordinate and advisor to very powerful military and civilian leaders.”

Powell arrived in Vietnam on Christmas Day 1962. It was the early days of U.S. military involvement in the ongoing conflict that pitted the communist North Vietnamese against the pro-Western government of the South.

In an effort to strengthen the South Vietnamese army’s response to the North’s guerilla attacks, President John F. Kennedy sent thousands of “military advisors” to Vietnam from 1961 to 1963. Powell, a 25-year-old Army captain, was among them.

During his year-long tour, Powell was a tactical advisor to three different South Vietnamese army commanders, and he adapted his supporting role to fit each man’s personality, writes Matthews. When the commander was effective, Powell stepped back into soldier mode, often personally leading dangerous counterinsurgency raids. But when one Vietnamese commander lacked rapport with his men, young Powell stepped in to win the confidence of his 400 troops.

“I was supposed to be an advisor, not the leader,” Powell wrote in his 1995 memoir My American Journey. “Nevertheless, the two of us were in quiet collusion. Leadership, like nature, abhors a vacuum. And I had been drawn in to fill the void.”

A loyal and unquestioning soldier, Powell didn’t hesitate to participate alongside the South Vietnamese when they torched enemy villages, killed livestock and burned fields, but he drew the line at corpse mutilation, writes Matthews, banning the practice of cutting off the enemy’s body parts as trophies.

Powell’s first tour was cut short when he stepped on a North Vietnamese booby trap called a punji spike. The sharpened stick was smeared with buffalo excrement to increase the odds of a deadly infection.

“The Special Forces medics cut my boot off, and they could see my foot was purple by then,” Powell later said in an interview. “The spike had gone all the way through, from the bottom to the top, and then come right back out, totally infecting the wound.”

In between Powell’s first and second tours in Vietnam, the career soldier enrolled in a series of prestigious officer training programs and repeatedly graduated at the top of his class. Powell redeployed to Vietnam in 1968 as a battalion staff officer with the Americal Division stationed in Duc Pho, a Viet Cong stronghold where American soldiers suffered heavy casualties.

Powell quickly impressed his superiors, including Maj. Gen. Gettys. After only three months on the job, Powell was promoted from mostly bureaucratic duties to become Gettys’ interim operations and planning officer, a job typically reserved for the most experienced officers.

“Overnight,” Powell wrote in his memoir, “I went from looking after eight hundred men to planning warfare for nearly eighteen thousand troops, artillery units, aviation battalions, and a fleet of 450 helicopters.”

Powell exhibited bravery and sense of duty during the helicopter rescue in November 1968, but he also showed some rare character flaws during his second tour in Vietnam, says Matthews.

Months before Powell was assigned to the Americal Division, members of the same infantry brigade perpetrated perhaps the most horrific crime against Vietnamese civilians during the entire war. What became known as the My Lai massacre entailed the murder of more than 500 unarmed civilians—including women, children and infants—in the captured village of My Lai. When rumors began to spread of a possible atrocity committed by U.S. soldiers, the army called for an internal investigation and Powell was one of the officers tasked with looking into the charges.

“This was still early in the Army’s cover up of what happened, but Powell wrote a pretty simple, glossy overview saying that there was no evidence of any kind of massacre,” says Matthews. “He literally said that relations between the American forces and the South Vietnamese people were ‘excellent,’ which was hardly the truth.”

Matthews says that Powell later admitted that his career ambitions and a desire to preserve his reputation as a loyal officer likely influenced his thinking during the war, but he also blamed the atrocities committed by all sides to the awful realities of war.

More than 58,000 U.S. servicemen died during the decade-long war in Vietnam. Following the withdrawal of U.S. troops in 1973, U.S. military leadership was forced to reassess its decision to intervene in other countries’ civil wars. The consensus that emerged became known as “Vietnam Syndrome,” says Christopher O’Sullivan, a history professor at the University of San Francisco and author of Colin Powell: A Political Biography.

“After Vietnam, the fear was that every deployment would become another Vietnam,” says O’Sullivan. “This had a powerful influence on Caspar Weinberger, Reagan’s Secretary of Defense, who wanted to make the criteria for deploying troops much steeper.”

In a 1984 speech, Weinberger laid out what became known as the “Weinberger doctrine,” a six-part criteria for using military force to resolve an international conflict. Powell worked under Weinberger and the two had a “father-son relationship,” says Matthews. They came to share the same conviction about the use of military force as a last resort. But once military force was required, it should be overwhelming and decisive.

“We couldn’t fight another war like Vietnam that had unclear objectives,” says Matthews, “that didn’t have the full support of the American people, and that didn’t send a decisive overwhelming force when the war broke out.”

When Powell was chair of the Joint Chiefs of Staff under President George H.W. Bush, he polished Weinberger’s principles into the “Powell Doctrine” and deployed it with spectacular efficiency, first in toppling Manuel Noriega’s regime in Panama in 1990 and then swiftly defeating Saddam Hussein’s forces in the first Persian Gulf War.

One of the most important lessons that Powell learned from Vietnam, says Matthews, was that senior military advisors needed to stand up and disagree with the president, “which the chair of the Joint Chiefs did not do during the Vietnam War.”

In the planning of the Persian Gulf War, President Bush and his Secretary of Defense Dick Cheney wanted to attack almost exclusively with air power, but Powell strongly disagreed.

“Powell said this would be another missed lesson from Vietnam,” says Matthews. “We need to go in with a decisive overwhelming force of ground troops, which they ultimately did. And after the Persian Gulf War, President Bush declared that the Vietnam Syndrome was over.”