Robert L. Allen, who definitively told the story of 50 Black sailors who were convicted of conspiracy to commit mutiny for refusing to continue to load munitions onto cargo ships after explosions had blown apart two ships at a California port during World War II, killing hundreds, died on July 10 at his home in Benicia, in Northern California. He was 82.

Mr. Allen, a writer, activist and academic, died a week before the Navy exonerated the men. His former wife Janet Carter said the cause was kidney failure. “The secretary of the Navy called to offer condolences,” Ms. Carter said in an interview, referring to Carlos Del Toro. “And he said, ‘I’m going to do more than that — I’m going to exonerate these sailors.’” Ms. Carter, who remained close to her former husband, a writer, activist and academic, added, “I cried in part because Robert wasn’t here to see it.”

On the night of July 17, 1944, hundreds of sailors were loading ordnance and ammunition onto the E.A. Bryan at the Port Chicago Naval Magazine, northeast of San Francisco. Suddenly, the munitions in the holds detonated, destroying the ship, the pier and structures within a 1,000-foot radius. Another ship, the Quinault Victory, blew apart and sank nearby in Suisun Bay. The blasts killed 320 sailors, civilians and Coast Guard personnel, most of them Black. Nearly 400 were injured, most of them also Black.

White officers were given leave to recover, but Black sailors were soon ordered to continue their dangerous work loading munitions at a nearby port. They did not know why the ships had exploded — a cause has never been determined — and 258 refused to keep working, Mr. Allen said, leading an admiral to threaten to execute them by firing squad. The Black sailors were arrested and taken to the hold of a barge that had room for 75 men.

“The scene conjured up images of a slave ship,” Mr. Allen told The Sacramento Bee in 1997. Of the 258 men, 208 returned to work, but they were still court-martialed for disobeying orders. The 50 others, in a summary court-martial, were convicted of conspiracy to commit mutiny and sentenced to eight to 15 years of confinement. One of the sailors, Martin Bordenave, told Mr. Allen: “How could it be a mutiny? I didn’t talk to nobody. I didn’t conspire with nobody. I just made up my mind, I was tired of it, you know. I wanted to be a sailor.”

In early 1946, 47 of the 50 men were released from prison under pressure from the National Negro Council and the Urban League, as well as from Eleanor Roosevelt and Thurgood Marshall, the future Supreme Court justice who was chief counsel of the N.A.A.C.P. at the time and had attended the trial. In an appeal, Mr. Marshall argued before the judge advocate general in 1945 that the men had at worst disobeyed an order but had not mutinied, and that they should be exonerated. “I can’t understand why, whenever more than one Negro disobeys an order, it is mutiny,” he said. Their convictions were upheld, but the publicity over the episode was a catalyst for the desegregation of the Navy in 1946. In clearing 256 of the 258 men (the convictions of the others had been previously set aside, one for mental incompetency, the other for insufficient evidence), Secretary Del Toro said that the defendants had been denied a meaningful right to counsel and that they had been improperly tried together despite conflicting interests.

Mr. Allen was a professor of ethnic studies at Mills College in Oakland, Calif., when he first heard about the Port Chicago case. In the late 1970s, he discovered a faded pamphlet in a library in San Francisco with a picture of Black sailors on its cover under the title “Mutiny?” (The pamphlet had been written by a reporter for a left-wing newspaper at Mr. Marshall’s request.) Over the next decade, Mr. Allen traveled by bus to interview survivors, some of whom were too ashamed of their mutiny convictions to have told their families. He obtained the transcript of the mutiny trial, scoured documents in federal archives for information on Port Chicago and found Mr. Marshall’s paperwork on the case. He received a Guggenheim fellowship, which helped finance his research.

His book on the episode, “The Port Chicago Mutiny: The Story of the Largest Mass Mutiny Trial in U.S. Naval History,” was published in 1989.“I don’t think you can overstate the significance of the interviews that he did,” Regina Akers, a historian with the Naval History and Heritage Command, said in an interview. She added, “He gave them a chance to capture their perspective in that season of their lives, about what happened to them and what it was like to be in the Navy — the work they did loading ammunition and the discrimination they faced.” Robert Lee Allen Jr. was born on May 29, 1942, in Atlanta. His mother, Sadie (Sims) Allen, was a teacher at Spelman College. His father was a mechanic. Both were community activists. Robert, who grew up in segregated Atlanta, was 13 when Emmett Till, then only 14, was tortured and murdered by white men in Mississippi in 1955. Robert learned about the killing through an article in Jet magazine and the horrifying pictures that accompanied it. “This is when I realized that the white people were not only dangerous, but they were dangerous to all of us, including me, because he was my age,” Mr. Allen said, referring to Emmett Till, in an oral history interview in 2019 with the University of California, Berkeley, where he taught.