John Prados, Master of Uncovering Government Secrets, Dies at 71

John Prados, a military historian whose dogged pursuit of classified government material led him to write dozens of books upsetting accepted truths about the Cold War, Vietnam and the American intelligence community, while also achieving renown as an award-winning board-game designer, died on Tuesday in Silver Spring, Md. He was 71.

His partner, Ellen Pinzur, said the cause of death, at a hospital, was cancer.

A self-described product of the 1960s who, with his ropy ponytail and bushy mustache, certainly looked the part, Dr. Prados was both a scholar and an activist.

As a historian, he wrote thick, deeply researched books on subjects as varied as the Battle of Leyte Gulf during World War II, the success of the Ho Chi Minh Trail during the Vietnam War, and the White House’s maneuverings before the 2003 Iraq war.

Running through all his work was the contention that records of intelligence and covert activities represented a sort of historical dark matter: a vast amount of material that, while invisible in conventional narratives, could, if revealed, radically shift our understanding of the past.

Across several books about the Pacific Theater in World War II, for example, he demonstrated that the American command of everyday intelligence — where Japanese forces were, where they were going — was just as important as the sheer firepower the United States brought to the fight.

His goal, he wrote in “Combined Fleet Decoded: The Secret History of American Intelligence and the Japanese Navy in World War II” (1995), was to “reassess the outcomes of battles and campaigns in terms not just of troops or ships but of how the secret war played out.”

For decades after World War II, such information was virtually impossible to access. Dr. Prados was still a graduate student at Columbia University when, in the 1970s, historians and journalists began taking advantage of the Freedom of Information Act to crack open government archives.

But going through the material was a slog, especially before digitization. Only a few people had the fortitude for it. Dr. Prados was one.

“He was an archives rat,” said Thomas Blanton, the director of the National Security Archive, where Dr. Prados was a senior fellow. “He was the ultimate prospector in the primary-source gold mine.”

Though he held a doctorate from Columbia, Dr. Prados never held a full-time academic position. Still, he was respected by academic historians and accepted into professional organizations, including the Society for Historians of American Foreign Relations.

“John was astonishingly productive, but what stands out in his work is the attention to detail,” Fredrik Logevall, a historian at Harvard, said in an email. “He was ever on the hunt for new sources, for the latest declassified documents, and he put them to expert use in his books.”

Dr. Prados was driven by more than intellectual curiosity. As a young man in the early 1970s he had been shocked by the extent of official perfidy revealed by documents like the Pentagon Papers and events like the Watergate scandal, and he believed that democracy hinged on the public’s access to government secrets.

Like other scholars and journalists who utilized the Freedom of Information Act, he worried that the lessons learned by his generation, coming out of the 1960s, were being forgotten in the 1980s, just as the Reagan administration was pushing secret wars in Central America and illegal deals like the one revealed by the Iran-contra affair.

“The American people not only have a need but a right to know their history,” he told The New York Times in 1993.

John Frederick Prados was born in Queens on Jan. 9, 1951 — the same birthday as President Richard M. Nixon, he often noted, with a mix of humor and horror. When he was in middle school his father, Jose Prados-Herrero, moved the family to San Juan, P.R., where he took a job with a sports arena. John’s mother, Betty Lou (McGuire) Prados, taught English as a second language.

John graduated from high school in Puerto Rico, then returned to New York to attend Columbia. He received a bachelor’s degree in political science and international affairs in 1973 and a doctorate in political science in 1982.

His dissertation, about the successes and failures of American intelligence assessments of Soviet military power, became his first book, “The Soviet Estimate: U.S. Intelligence Analysis and Soviet Strategic Forces,” published in 1982.

His marriage to Jill Gay ended in divorce. Along with his partner, he is survived by his daughters from his marriage, Dani and Tasha Prados; his brother, Joe; and his sister, Mary Prados.

After years spent collaborating with the National Security Archive, he joined the organization as a senior fellow in 1997. He soon became its most visible and vocal figure, quick with a quotation or research tip for a like-minded journalist, especially after the terrorist attacks of Sept. 11, 2001 and the Iraq war, events that he feared would herald a new era of government secrecy.

Dr. Prados liked to say that his love for researching and writing was closely related to his second passion: designing board games that intricately simulated historical military conflicts. He created more than 30 such games, with titles involving the Napoleonic Wars, World War II and, of course, Vietnam.

Many of his games have come to be regarded as classics of their genre, none more so than “The Rise and Decline of the Third Reich” (1974), a globe-spanning strategy contest in which players, as the different warring nations, balance economic and military resources against the chance of a dice roll. The game won a Charlie award, the top honor in war game design.

Fans of the game were legion, and far-flung: The Chilean author Roberto Bolaño created a character who mastered it in his novel “The Third Reich.”