While many people trace the dawn of the nuclear era to August 6, 1945, and the dropping of the atomic bomb over Hiroshima, it really began three weeks earlier, in the desert near Alamogordo, New Mexico, with the top-secret Trinity test, on July 16, 1945. This forms the dramatic center of Christopher Nolan’s new “Oppenheimer” epic, coming to theaters on July 21. That has been true, in fact, about every movie about the making and use of the first atomic bomb, going back to the very first film in 1947.

The successful detonation put President Truman on the path to using the horrendous new weapon, twice, against Japanese cities, killing at least 170,000 civilians and others. Much less attention has been directed at how the aftermath of the test lay the groundwork for the age that would follow: the cover-up of radiation effects on Americans (workers, soldiers and others) and government obsession with secrecy, soon extending to all military and foreign affairs in the Cold War era, with many negative effects.

One value of focusing on the New Mexico bomb test and not Hiroshima and Nagasaki in popular accounts: No one died that day at Trinity, a far cry from what would happen in Japan. In finalizing work on the revolutionary new weapon, Manhattan Project scientists knew it would produce deadly radiation but weren’t sure exactly how much. One Los Alamos scientist had already died from radiation exposure. The military planners were mainly concerned about pilots ion the bombers carrying the payload catching a dose, but Robert Oppenheimer, the scientific director of the Manhattan Project, worried, with good cause (as it turned out) that radioactive particles could drift for miles and fall to earth, especially with the rain.

Scientists warned of dangers to those living downwind from the Trinity site but, in a pattern-setting decision, the director of the bomb project, General Leslie R. Groves, ruled that residents should not be evacuated and kept completely in the dark (even after they were sure to spot a blast brighter than any sun before dawn on July 16). Nothing was to interfere with the test. When two doctors on Oppenheimer’s staff proposed an evacuation, Groves replied, “What are you, Hearst propagandists?”

There is no record of Oppenheimer himself trying to intervene. Most movie and book portrayals of him — we don’t know yet about Christopher Nolan’s — focus on him leading the drive to make the bomb but downplay his role in advocating its use against Japan. In fact, he was militant on getting the bomb used against Japan, even taking part in targeting decisions.

Admiral William Leahy, President Truman’s chief of staff — who opposed dropping the bomb on Japan — placed the weapon in the same category as “poison gas.” Sure enough, soon after the shot went off, scientists monitored alarming evidence. Radiation was quickly settling to earth in a band thirty miles wide by 100 miles long. A paralyzed mule was discovered twenty-five miles from ground zero.

Still, it could have been worse. The cloud had drifted over loosely-populated settlements. “We were just damn lucky,” the head of radiological safety for the test later affirmed. The local press knew nothing about any of this. When the shock wave had hit the trenches in the desert, Groves’ first words were: “We must keep the whole thing quiet.” These seven words set the tone for the decades that followed.

Naturally, reporters from nearby newspapers were curious about the big blast, however, so Groves released a statement written by W.L. Laurence (who was on leave from the New York Times and playing the role of chief atomic propagandist) announcing that an “ammunition dump” had exploded. Nobody questioned and the bomb project and preparations for using the weapon in war accelerated.

In the weeks that followed, ranchers discovered dozens of cattle had odd burns or were losing hair. Oppenheimer ordered post-test health reports held in the strictest secrecy. When Laurence’s famous report for The Times on the Trinity test was published after the Hiroshima bombing he made no mention of radiation.

Even as the scientists celebrated their success at Alamogordo on July 16, the first radioactive cloud was drifting eastward over America, depositing fallout along its path. When Americans found out about this, three months later, the word came not from the government but from the president of the Eastman Kodak Company in Rochester, New York, who wondered why some of his film was fogging and suspected radioactivity as the cause.

Fallout was absent in early press accounts of the Hiroshima bombing as the media joined in the triumphalist backing of The Bomb and the bombings. It was pictured as just a Big Bang. When reports of thousands in Hiroshima and Nagasaki afflicted with a strange and horrible new disease emerged, General Groves called it all a “hoax” and “propaganda” and speculated that the Japanese had different “blood.” He told a congressional committee that he had heard that expiring from radiation disease was a rather “pleasant way to die.”

None of this made an appearance in 1947 when Hollywood produced its first movie on the atomic bomb, MGM’s “The Beginning or the End.” In one scene before the Trinity test, General Groves even cracks a joke when someone wonders what would happen if the bomb created a radioactive cloud. “I don’t know about you,” Groves (Brian Donlevy) comments, “but I am running.”

The movie also stayed clear of the famous line uttered by Oppenheimer after the blast, from the Baghavad Gita, “I am become death, destroyer of worlds,” and the claim by a fellow scientist that morning: “Now we are all sons of bitches.” Instead we see Oppenheimer, Groves and others striding across the desert, chatting about how President Franklin Roosevelt would be so proud if he had lived to see this day.

My recent book, “The Beginning or the End,” also explores how Oppenheimer signed a release for MGM allowing himself to be depicted in the movie (and serve as narrator) even after reading a script and considering it awful and full of falsehoods. Truman and the Pentagon forced the filmmakers to introduce pro-bomb revisions, even if many were inaccurate.

We’ll soon see if Nolan includes any of this in his new movie. When some of the truth about radiation and radiation disease started to surface in the U.S. media, a full-scale official effort to downplay the death toll from that really enveloped the issue, so as not to alarm Americans now facing their own nuclearized future. Oppenheimer even led a misleading press tour of the Trinity site a month after the atomic attacks to “give lie to”(as the Pentagon put it) Japanese claims of radiation dangers. Of course, Geiger counters found only low levels of radiation lingering at the test site, which hardly disputed the initial dangers.

Yet few could escape the threatening, sometimes tragic effects, for decades: millions of workers in the nuclear industry, “downwinders” near the test sites (and others exposed to fallout across the country), and “atomic soldiers and sailors” asked to witness tests at close hand, among others (not to mention the American patients subjected to medical tests). The mindset of “secrecy first” took hold throughout the government, with obvious ramifications for us today.

Trinity was the beginning, but we are not yet at its end.

Greg Mitchell’s latest book is “The Beginning or the End: How Hollywood–and America–Learned to Stop Worrying and Love the Bomb”( (The New Press). He has written a dozen books and has directed three documentary since 2021, including Atomic Cover-up, and two for PBS.