"Archives Rat" John Prados Punctured Military Secrecy to Write History

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.