American planners kept Hiroshima and four other cities off the firebombing lists through the summer of 1945 so the new weapon could be measured against something intact; the people living there had spent months wondering why the raids never came

By mid-1945 American bombers had worked down the list of Japanese cities by size, from Tokyo to towns of thirty thousand. Hiroshima, seventh largest in the country, had never been hit in strength. That was not luck.

John Hersey, who went there the following spring for the New Yorker, found a city that had spent months uneasy about it. B-29s came over almost nightly; the fleets used Lake Biwa as a rendezvous and crossed the coast nearby whatever they meant to burn. The sirens went. Nothing came. A rumor was going around, Hersey wrote, that the Americans "were saving something special for the city."

They were, and a committee had settled it months earlier.

Why Hiroshima had not been bombed

The Target Committee met three times that spring: in Washington on 27 April, at Los Alamos on 10 May, and in Washington again on 28 May. Leslie Groves took the chair over a room that mixed soldiers with physicists: John von Neumann, Robert R. Wilson, the British physicist William Penney.

Two of the conditions they set are what anyone would expect: a target more than three miles across and important within a large city, and a blast that could damage it.

The third shaped the whole summer. The place had to be one that was unlikely to have been attacked by August.

That is a measurement problem wearing the clothes of a targeting rule: nobody can say what one bomb did to a city that has already burned twice. So the committee's five nominations (Kokura, Hiroshima, Yokohama, Niigata and Kyoto) went to the Army Air Forces with a request to leave them off the incendiary rounds, and the Air Forces agreed.

The city Stimson took off the list

At the end of May, Secretary of War Henry Stimson asked for Kyoto to be struck for its historical and religious importance. Groves argued back, rating the city highly for its size and industry. Stimson went over him to Truman, who agreed; it is the only one of these targeting decisions the president is known to have taken himself.

The story usually attached to this is that Stimson had honeymooned in Kyoto and could not stand to see it burned.

Alex Wellerstein, a historian of the Manhattan Project, took that apart in 2023. Stimson married in 1893 and did not lay eyes on Kyoto until 1926, on a fact-finding trip through Asia, then stayed one night in 1929 on his way home from the Philippines. Wellerstein traces the honeymoon to British newspaper writing around 2002, with nothing under it.

The correction earns its keep, because the Stimson of the diaries wants something other than a keepsake. He argues that burning Kyoto would sour Japanese opinion of the United States for a generation and shove the country toward the Soviets after the war. That is not sentiment; it is postwar policy, and it applied to every city on the list. It was granted to one. Nagasaki took Kyoto's place in late July.

What was actually in Hiroshima

An army, and a large one.

The Second General Army had its headquarters in the grounds of Hiroshima Castle under Field Marshal Shunroku Hata, the command responsible for defending western Japan against the invasion everyone knew was coming. Ujina, the port on the city's south edge, had been shipping soldiers overseas since the war with China in the 1890s. The garrison is usually put at around 24,000.

By 1945 standards that is a genuine military target, and it accounted for a small share of the people the bomb killed. The city's own count puts about 350,000 people there that morning, and roughly nine in ten of the dead were civilians. Both facts hold at once, and nothing in the criteria asked anyone to weigh them: what a target needed was to be large and undamaged. Hata was in the castle grounds when it went off, survived, and ran the relief effort.

The morning of August 6

Hiroshima's sirens had already run twice before dawn. An alert at 12:25 a.m. was cleared at 2:10. At 7:09 they went again for a single aircraft, the weather plane Straight Flush, and the all-clear came at 7:31.

The Enola Gay had left Tinian at around 2:45, with Captain William Parsons of the Navy finishing the weapon's assembly by hand in the bomb bay: loaded B-29s kept crashing on takeoff from that runway, and he had no intention of taking the island with him.

Close to eight, radar operators counted the incoming aircraft and made it three. Three was not worth an alarm: a formation that small read as reconnaissance, and the radio said only that shelter might be advisable if B-29s were actually seen.

Thomas Ferebee released the bomb at 8:15 from about 31,000 feet, aiming at the T-shape of the Aioi Bridge. It fell for 43 seconds and went off some 2,000 feet above the Shima surgical clinic, a few hundred feet from his aim point. About 140,000 people were dead by the end of December, on the city's own estimate.

Tokyo learned of it slowly, and from the enemy. The radio station in Hiroshima went off the air and the telegraph line north of the city stopped working; the General Staff, unable to raise anyone there, sent an officer to fly down and look, and he saw the smoke from a hundred miles out. Truman's announcement in Washington, sixteen hours later, told them what it had been.

The building the city argued about for twenty years

Jan Letzel, a Czech architect working in Japan, finished the Hiroshima Prefectural Commercial Exhibition hall in April 1915, with an oval dome of copper sheet over a steel frame. The bomb went off almost directly overhead, 500 feet to one side and 2,000 feet up, which is why its walls stayed standing when everything around them went flat: the blast came from above rather than from the side.

Holding the ruin up cost money, it might come down on somebody, and plenty of the people who walked past it daily wanted it gone.

A diary settled it. Hiroko Kajiyama, an infant in the city when the bomb fell, wrote on the anniversary in 1959 that the wrecked hall was the one thing left that would keep telling the world what had happened there. She went into the hospital in March 1960 and died the following month of acute leukemia. Schoolchildren who had read it formed the Hiroshima Paper Crane Club and began collecting signatures and money to save the building.

A 1965 survey found it could be held up after all, the council passed its preservation resolution on 11 July 1966, and donations came to 66,197,816 yen. UNESCO listed the site in December 1996.

What is left to argue about

The dome is the easy part. It gets surveyed and braced on a cycle, and it will outlast everyone who saw it happen.

The survivors are the part no repair schedule covers. At the end of March 2026, 91,105 people held an atomic bomb survivor's certificate, down 8,025 in a year, at an average age of 86.66. In 1981 there were 372,264. The Nobel Peace Prize went in 2024 to Nihon Hidankyo, the survivors' confederation founded in 1956, and the citation was about witness testimony rather than advocacy.

There is a hard symmetry in that, given how the city was picked. Hiroshima went on the list partly because it was still whole, so the effect of one bomb could be read off it cleanly. The reading was done by the people who lived there, and they have been the ones reporting it ever since. Within a decade the job passes to people who were never in the city, working from recordings, from archives, and from a building Hiroshima nearly tore down.

Sources

• John Hersey, Hiroshima (1946), the New Yorker article in its Penguin edition
• Manhattan Engineer District, The Atomic Bombings of Hiroshima and Nagasaki (1946), via atomicarchive.com
• City of Hiroshima, "The Realities of the Atomic Bombing" and "Preservation of the Atomic Bomb Dome"
• Alex Wellerstein, "Henry Stimson didn't go to Kyoto on his honeymoon," Restricted Data (2023)
• Chugoku Shimbun, Hiroshima Peace Media Center, on Hiroko Kajiyama and on hibakusha certificate figures
• Wikipedia, "Atomic bombings of Hiroshima and Nagasaki" and "Shunroku Hata"