The atom bomb: on the 70th anniversary of Hiroshima and Nagasaki, a look at the long shadow of nuclear war.

• Author: Majerol, Veronica
• Position: TIMES PAST 1945

On Aug. 6, 1945, 8-year-old Shigeaki Mori was walking across a bridge on his way to summer classes when "suddenly, I felt a massive shock wave and a blast from above," he recalled recently. That blast, which obliterated Mori's hometown of Hiroshima, Japan, was caused by the world's first-ever nuclear attack.

Mori was blown off the bridge and into a shallow river. When he regained consciousness, nearly everything around him was enveloped in thick black smoke, and the few things Mori could see, like a woman walking toward him, were horrifying.

"She was swaying ... and holding something white," he said. "I realized she was holding the contents of her stomach. " The United States dropped an atomic bomb on Hiroshima--and three days later on the Japanese city of Nagasaki--70 years ago to force Japan to surrender and end World War II (1939-45). The bombings killed as many as 250,000 and led to Japan's official surrender three weeks later, which arguably saved many thousands of American lives.

But dropping those bombs also had long-lasting consequences for the U.S. and the world that plague us today. In the years since, more nations have developed their own nuclear arsenals. Today, the threat of an attack by rogue nations like North Korea or Iran--or from a terrorist group that gets its hands on a bomb--remains a terrifying security problem for the U.S. and the world, with no easy solution.

Einstein's Letter

How did the U.S. come to possess the most destructive weapon the world had ever known? It started with a letter that physicist Albert Einstein wrote to President Franklin D. Roosevelt on Aug. 2, 1939--a month before Nazi Germany invaded Poland and started the Second World War. Einstein, a Jew who had fled Germany in 1933, warned Roosevelt about the potential destructive power of a nuclear weapon. He urged the president to fund a project to develop an atomic bomb--and quickly, before Germany's dictator Adolf Hitler beat him to it.

Roosevelt heeded Einstein's warning and partnered with Britain and Canada to recruit thousands of scientists to collaborate on the Manhattan Project (so named because it began in an obscure office in New York City). Stationed at isolated sites in Tennessee, Washington State, and New Mexico beginning in 1942, the scientists worked feverishly to figure out how to unleash the enormous amounts of energy contained in atoms. Einstein had first theorized the relation between matter and energy in his 1905 equation E = mc2 (see Timeline, p. 20). Because other countries, like the Soviet Union, Germany, and Japan, were also racing to develop an atomic weapon, the Manhattan Project was kept top secret.

Roosevelt never got to see the project's completion. He died on April 12, 1945. Shortly after, Secretary of War Henry Stimson sent President Harry S. Truman a brief memo referring to "a highly secret matter" that "has such a bearing on our present foreign relations ... that I think you ought to know about it without much further delay." (Truman had become vice president in January 1945, but Roosevelt had never told him about the Manhattan Project.)

The first test to see whether the bomb worked took place on July 16, 1945, with scientists and military experts gathering at Alamogordo, New Mexico. Just before dawn, a giant fireball exploded into a mass of dust and gaseous iron, soaring a mile a minute and forming a mushroom cloud. The blast carved a 1,200-foot crater in the desert floor. The blinding light and enormous roar traveled hundreds of miles.

The atom bomb came too late to affect the war in Europe, where more than 300,000 American soldiers had died; Germany had already surrendered in May. But fighting still raged in the Pacific, and Japan--which drew the U.S. into World War II by attacking Pearl Harbor in Hawaii on Dec. 7,1941--showed no signs of giving up. Dropping the atomic bomb as opposed to committing U.S. troops to an invasion of mainland Japan would save half a million lives, Truman said. America's use of the atom bomb--to this day, the only time it was ever used--is still controversial (see Debate, p. 22).

"The Americans had concluded that the Japanese, [with] their kamikaze suicide attacks and their refusal to surrender--you couldn't fight people like that with anything but full measures," says Christopher Hamner, a history professor at George Mason University in Fairfax, Virginia.

On August 6, an atomic bomb-named Little Boy by one of the nuclear physicists--was dropped on Hiroshima, a city of several hundred thousand people in southern Japan. Nearly 70 percent of the city's buildings and houses were leveled or irreparably damaged. The War Department (today the Defense Department) said the bomb packed more explosive power than 20,000 tons of TNT.

"The force from which the sun draws its power has been loosed against those who brought war to the Far East," Truman declared.

Three days later, a second bomb, called Fat Man, was dropped on Nagasaki, about 200 miles southwest (see map, p. 19). The two bombs killed between 150,000 and 250,000 people--some immediately and some from radiation sickness later on.

On August 15, Japan accepted the Allies' peace terms, and on September 2, it formally surrendered, finally ending World War II.

The Cold War

After the war, America found itself embroiled in a...