Fifty years ago, Coretta Scott King addressed Harvard's graduating seniors on Class Day in her slain husband's place. Martin Luther King Jr. had been assassinated two months before and, just a week before, so had Robert Kennedy.

On that June 12, a mourning King wore a black suit as she spoke to more than 1,300 students — all men and almost all white — who crammed into Harvard’s dim and cavernous Sanders Theater. The school did not admit women until 1977. She suggested the students had been deeply affected by the loss of two men she called “champions of freedom, of justice, of human dignity and peace." And she predicted that the country was “swiftly moving toward self-annihilation.“

King urged the young Harvard students, dressed in black graduation robes and neckties: “Your generation must speak out with righteous indignation against the forces seeking to destroy us.”

Watch: Coretta Scott King speaks at Harvard's Class Day in 1968

The Class Day speech was the latest in a series of speeches King had given in the months after the staggering personal and national tragedy of her husband's death, said Jeanne Theoharis, a historian of the civil rights movement who teaches at Brooklyn College.

“That she is able to do this, also speaks to the depth of her own politics," Theoharis said. In fact, she added, it was King who had pushed her reluctant husband long before the Harvard speech to openly stand against the Vietnam War.

"She does step in for him," noted Theoharis, "but in many ways, in terms of Vietnam, she's out in front of him on Vietnam. She's out publicly years before him."

In her speech, Coretta Scott King even called out President Lyndon Johnson on the war, garnering long and loud applause.

"This war, which is the most cruel and evil war in our history, must come to any end. I call upon the president of the United States to stop the bombing in Vietnam now," she said.

Henry Norr introduced King before her speech to his classmates. Looking back, Norr said, "between the urban turmoil, and the war, and the draft resistance, and the assassinations, it was a world gone spinning out of control."

For the hundreds of privileged young white men listening on that day so soon after her husband's assassination, Norr said, she had become a powerful symbol "of the hopes we had for a better America, and the sense that there would be casualties. It was a very tough time ... emotionally. I think probably for most Americans, but certainly for us who were graduating from college that year."

One can hardly imagine how tough the time was for King, who had just turned 41, with four young children, having lost her husband. Yet she was a picture of grace and courage. She expressed great optimism in white college students, saying no other generation was less racist, less materialistic and more against the war.

"The young understand this society better than their elders think," she said. "They listen to the preachments of authority on behalf of order against violence, and they know that the order evoked has been the very order which has done systematic violence to the poor and the colored for centuries."

Norr understood the ironies of those "preachments of authority." While many of his Harvard classmates would go on to positions of leadership and power, Norr, by his account, has led a somewhat ragtag life — with many false starts and stops, career-wise. What has tied it together from the '60s onward is a thread of protest against power wrongfully wielded.

But at least on June 12, 1968, he, like many of his young classmates packed into that stuffy hall, was stirred by Coretta Scott King's optimism in the face of chaos, as she lauded their "restless search for truth."