When my mother died, four years ago, my brother and I cleared out her apartment. Because I was going to handle her final tax returns, I took initial possession of her files.

Going through them was a melancholy task. Except for the financial records, I put it off. A few months ago, though, I finally culled through them.

They weren’t voluminous. Our mother was the opposite of a pack rat. When we checked her MacBook Air after her death, there were no personal files at all.

She had also thinned out her physical documents to the bone. Still, she had kept some paper correspondence of special significance. My father’s army letters back from Europe during World War II, for instance. (My dad died six years before her, in 2011.)

But while my brother and I were already generally familiar with the army letters, I did come across one document she had kept that neither of us had previously known anything about. It was a carbon copy of a letter my father had written in March 1956. It related to a dear friend of his, Herbert C. Kelman.

The author’s parents, Morris and Gloria Parloff, in 1943.

Though we didn’t see him often, Kelman, who taught at Harvard, had always been one of my favorites among my parents’ friends. He was soft-spoken, extremely articulate, and seemed to weigh carefully whatever I said, even as a child. As I remember it, he spoke with an unusual crispness that, in retrospect, must have been the trace of an accent. (He was born in Vienna in 1927, fled after the Nazis gained power, reached this country in 1940—at about age 13—and became a naturalized citizen.)

I also knew vaguely that he’d been active in the civil-rights movement and other social causes. (In the 1950s, he and his wife, Rose, helped launch the Baltimore chapter of the Congress of Racial Equality, which organized campaigns to integrate lunch counters.)

In March 1956, however, when the letter was written, Kelman was working at the National Institute of Mental Health, in Bethesda, Maryland. He was 28 at the time, and my father, Morris Parloff, 38, was one of his supervisors.

Morris Parloff’s 1956 letter opposing the firing of Herbert Kelman (inset).

The purpose of the letter was to save Herb’s job. Someone thought he was a Communist. A decision had already been made to fire him. Kelman had appealed to then secretary of health, education, and welfare Marion Folsom. My father was writing in support of his appeal.

Though I’ve known about the McCarthy era for as long as I can remember, I’d never thought about, on a granular level, what it would be like to write a letter like this one.

Someone thought he was a Communist. A decision had already been made to fire him.

Think about it. Someone fairly high up in the hierarchy of which my father was a part—presumably above him in rank—had already decided to fire Kelman. The specific allegations against him were unknown to my father—or, as the letter indicates, even to Kelman. Speaking out on Kelman’s behalf could not have been a risk-free proposition.

And had my father played it safe in that era, he’d have had plenty of company. A few years earlier, then presidential candidate Dwight Eisenhower, bowing to political calculations, famously deleted from a stump speech his planned defense of his friend General George C. Marshall against one of Senator Joe McCarthy’s smears.

But my father did weigh in, and I think he did a good job with the tricky assignment. My mother must have thought so, too, which might explain why she kept the letter for 61 years, until her death. (Knowing how my parents operated, I assume she edited it.)

My father spoke initially of the blow to N.I.M.H. if Kelman’s termination were to be upheld. Next, he focused on the adverse impact the firing would have on staff morale. “It will be difficult for those of his colleagues who are personally acquainted with him to persuade themselves that the action of the Public Health Service was well considered,” my father wrote.

Then the letter turned to a subject that may have placed Kelman under suspicion. He had taken conscientious-objector status during the recently concluded Korean War, fulfilling his military-service obligation through nonmilitary means. The way he had handled his draft status, however, actually further illustrated his singular integrity, the letter argued. At the same time that the draft board was reviewing Kelman’s C.O. request, the Public Health Service had granted Kelman a fellowship relating to his then work at a psychiatric clinic.

Recognizing the possible embarrassment his draft status might cause the service, Kelman had reported what was happening to the fellowship board in case it wished to postpone or retract the grant.

“This remarkable display of integrity and tact deeply impressed his colleagues as well as members of the Fellowship Board,” my father wrote. “The Fellowship was subsequently awarded to Dr. Kelman.”

Finally, my father addressed the loyalty issue head-on:

In addition to a close work relationship, Dr. Kelman and I have had considerable social contacts which have afforded us many opportunities to explore each other’s political views. I am firmly convinced of his loyalty. He is not simply “non-communist” but distinctly and emphatically “anti-communist.” His dedication to the principles of our democratic constitutional form of government is completely incompatible with any totalitarian views.... He has a full measure of courage which permits him to act in a manner consistent with his analysis of a situation and consistent with his basic democratic philosophy. He is neither a “starry-eyed” idealist nor a “wild-eyed” radical. He is, rather, a citizen who takes seriously his responsibilities to himself and to the community.

Dwight Eisenhower, bowing to political calculations, famously deleted from a stump speech his planned defense of his friend General George C. Marshall against one of Senator Joe McCarthy’s smears.

I wondered if the letter would be of interest to Kelman’s loved ones. An online obituary revealed, however, that his wife had died a year earlier and that they’d had no children.

Then I saw that there was a Herbert C. Kelman Institute in Austria devoted to “peacebuilding in international and intra-societal conflicts.” I wondered if they’d want to see it.

Finally, though, I found out that Herb himself is alive, at 94. As a professor emeritus, Kelman has a page on Harvard’s Web site. I e-mailed his assistant.

“Herb remembers you and your parents fondly and would love to read your father’s letter,” she responded. She advised me to mail it to the postal address of a senior-living center. She also forwarded to me an account Kelman had published about the incident in a professional newsletter in 1957.

It filled in the stark, missing details. In January 1956, Kelman was told he was being fired, effective one week later. He’d been found to be “unsuitable.” My father’s was one of five letters appended to Kelman’s appeal to Secretary Folsom. In May, the department’s “internal security” unit interviewed Kelman—for five hours—about his and his wife’s associations. In June 1956, Secretary Folsom rescinded the termination and apologized to Kelman.

Former president Obama recently observed that our nation’s “experiment in democracy is not self-executing.” That’s true, in fact, of all the treasured liberties our country affords. In small ways, we must step up when the moment arises. I had known about my father’s military service, but never about this other modest but fearless way in which he had served his country.

Glad my mother kept the letter.

Roger Parloff is a Washington, D.C.–based writer