John Hersey shunned publicity, gave few interviews throughout his life, and refused to go on press tours when any of his more than a dozen books came out. On the eve of the release of his biggest journalistic story—one of the most influential scoops of the 20th century—he left New York City altogether, taking up temporary residence in Blowing Rock, North Carolina. Hersey was a publicist’s nightmare, but the ultimate purist journalist; he never allowed himself to outshine his stories. Despite this, he became famous early on. He won the Pulitzer Prize at just 30 for his wartime novel, A Bell for Adano (1944), which was immediately pounced on by Hollywood and Broadway. During World War II, he was also commended as a war hero for helping to evacuate wounded Marines while covering a battle in Guadalcanal.

And then came “Hiroshima,” Hersey’s 1946 story for The New Yorker. Nearly a year after the U.S. dropped atomic bombs over Hiroshima and Nagasaki, Japan was still restricting access to the cities, making it virtually impossible for journalists—Japanese and foreign—to report on the bombs’ aftermath. Hersey got into Hiroshima regardless, managed to interview several dozen blast survivors there, and wrote in excruciating detail about their experience as some of the only human beings in the world to ever experience nuclear attack. The story took up nearly the entire August 31, 1946, issue of The New Yorker and created an international furor. Not only did it depict the human cost of the bombings; it also revealed the truth about the bombs’ radioactive qualities, which the U.S. government had tried both to downplay and cover up. Hersey would later claim that “Hiroshima” wasn’t meant to be an exposé, but it turned out to be precisely that.

In researching my new book, Fallout: The Hiroshima Cover-Up and the Reporter Who Revealed It to the World, I was determined to find out how in hell Hersey had gotten into Hiroshima. As the saying goes, whoever controls the ground, controls the story—and General Douglas MacArthur’s forces had dominated Japan by the time Hersey arrived, eight months into the occupation. The reporting in “Hiroshima” implied that Hersey had somehow gotten into the country and out again undetected by the beady eyes of the U.S. military. Yet what I discovered was that Hersey was not a unilateral reporter, coming into the country under the cloak of darkness. He had been, instead, the perfect Trojan Horse of war correspondents.

Into the Wardrobe

Hersey may have hated doing publicity, but he had an early sense of his own prominent place in history. When “Hiroshima” was published, he swiftly donated the first draft to Yale, his alma mater. (The Library of Congress also vied to acquire the document—alas, too late.) Yale’s Beinecke Library houses a substantial trove of his personal and professional materials as well. Within that trove: many of Hersey’s “Hiroshima” reporting materials, including cryptic, handwritten field notes scrawled in pencil on the back of envelopes.

At first, the names and places noted there made little sense to me, but they ended up being crucial in piecing together Hersey’s time on the ground in Japan. I learned that “Cable 2nd floor Radio Tokyo” meant someone had directed Hersey to General MacArthur’s press-relations office (and his censors) in the former Radio Tokyo building—pretty much the only place from which a reporter could file a story via cable at the time. No wonder, then, that Hersey and his New Yorker editors decided that he would write “Hiroshima” back in the United States. Also discovered in the Yale archive: clearance papers for Hersey to enter Japan in May 1946, issued by General MacArthur’s press-relations office. Hersey had applied as an accredited correspondent, was granted access, and even accepted military transport into the country. (It couldn’t have hurt that Hersey had, several years earlier, written an overly complimentary biography of General MacArthur.) This archival discovery undercut my original assumption that he had sneaked into the country. Records also revealed that two days after his arrival in Japan, he was given permission to travel, for a limited time, to Hiroshima.

Hersey helped to evacuate wounded Marines while covering a battle in Guadalcanal during W.W. II.

To be sure, neither Hersey’s war-hero status nor his glowing portrait of General MacArthur exempted him from scrutiny: documents revealed that he was closely monitored by MacArthur’s forces and that F.B.I. officials in both Japan and Washington, D.C., had been notified of his arrival. But the question still remained: Why was Hersey given access in the first place? For foreign reporters at the time, travel to Hiroshima and Nagasaki remained tightly controlled by SCAP (the Supreme Commander for the Allied Powers—General MacArthur’s operation), and the cities’ post-bomb fates were a tightly restricted topic. Parsing SCAP’s rationale became one of the challenges of my project.

Hersey had been the perfect Trojan Horse of war correspondents.

Yet more surprising revelations came from the New Yorker papers at the New York Public Library. Hersey’s editors—Harold Ross and William Shawn, one of the great odd-couple editorial partnerships in magazine history—were also well aware of the historical significance of “Hiroshima,” and preserved detailed project records.

That said, some of those records had since managed to get lost; others had been extensively picked over. My expectations for finding treasure there were low. Nevertheless, I made myself go through files that seemed irrelevant to the project, and on my last day there I found a misfiled document—tucked away in a file about wartime censorship—that made me stand up in the middle of that silent reading room and scream, “Holy shit.” The document revealed the previously unreported role that Lieutenant General Leslie R. Groves, head of the Manhattan Project, had played in the backstory of “Hiroshima.” It turns out that the New Yorker team had essentially been forced to submit their story to the War Department for censorship, or face possible jail time or worse if the government decided that Hersey’s reporting revealed proprietary nuclear secrets, as per nebulous “restricted data” standards put forth in the just passed Atomic Energy Act of 1946. It was akin to sending the article to the guillotine. But luckily for Hersey and his team, General Groves seemed to have found an unlikely, deeply cynical utility in “Hiroshima.” I’ll leave it at that for now.

Among the New Yorker papers I also came across a previously undetected or ignored clipping about how Hersey’s reporting was regarded by the Soviets. In short, they hated Hersey, they hated “Hiroshima,” and they even dispatched a Soviet “journalist” to Japan to debunk the revelations of Hersey’s story and downplay the Americans’ new mega-weapon. Clearly the Soviets were not enjoying their temporary nuclear disadvantage vis-à-vis their former American allies.

Apocalypse Now

I don’t know if Hersey would approve of Fallout. He did, from time to time, cooperate with early biographers and scholars (I have some of their interview notes) and gave a few important interviews around the time of the 40th anniversary of the Hiroshima and Nagasaki bombings.

But given that our free press is under unprecedented assault, and that our government is once again trying to downplay and cover up a deadly existential threat, Hersey’s story needed to be told, and quickly. He was hugely significant in 1946 and the decades that followed—a whistleblower who showed the world what nuclear warfare truly looks like—and his portrait of post-apocalyptic devastation in “Hiroshima” has long served as a pillar of deterrence in preventing more nuclear attacks. His significance now, as a reminder of how crucial investigative reporting is when it comes to holding the powerful to account, is just as great.

In the aftermath of World War II, Hersey and many of his Allied war-reporter colleagues saw America’s free press as crucial to the survival of democracy—a form of government which had then just narrowly escaped extinction. Our democracy is imperiled now, and Hersey is, once again, an important North Star of truth-seeking and decency.

So, my conscience as the biographer of this reticent subject is clean.

Lesley M. M. Blume’s Fallout: The Hiroshima Cover-Up and the Reporter Who Revealed It to the World is out now from Simon & Schuster