"Sixteen hours ago an American airplane dropped one bomb on Hiroshima, Japan, and destroyed its usefulness to the enemy. The bomb had more power than 20,000 tons of T.N.T. ..."

With those words, President Harry Truman unveiled the nuclear age.

The world would never be the same again.

The atomic bombing of Hiroshima on Aug. 6, 1945, stands as one of the most extraordinary and most controversial accomplishments in the history of mankind. The atom was long revered as a source of vast, limitless power. It had finally been harnessed -- and unleashed on a civilian population as a weapon.

There may be much to answer for with this act, and perhaps even more so with the bombing of Nagasaki three days later. Why drop two atomic bombs? Some historians believe the United States was proving its might and demonstrating the futility of resistance to Japan's emperor in no uncertain terms. Others speculate America was sending a message to the Soviet Union that it had the power to keep the expansive communists in check -- one way or another.

Truman made the decision to use the bomb after considering the casualty projections for a proposed invasion of Japan. Since mid-1942, Allied forces had worn down the Japanese military, pushing it back across the Pacific and sweeping it out of a thousand islands and atolls. Japan's military and civilian population were digging in for a desperate final stand. By all indications, an Allied invasion would have resulted in a long, murderous campaign.

Thus, Truman said yes to the bomb.

Hiroshima was the first to feel the atomic wrath.

At about 8 a.m. local time on Aug. 6, Japanese radar detected high-altitude aircraft approaching and issued air raid alerts in several cities, including Hiroshima. When radar detected just three planes, the alerts were lifted; it was believed to be a reconnaissance mission. Radio broadcasts recommended that people might want to head to shelters should any B-29s actually be sighted.

At 8:15 a.m., the bomb was dropped. It exploded over the city.

There was a blinding flash -- so bright and intense that it literally melted the eyeballs of those near ground zero who were looking directly at the explosion at that instant -- followed by a powerful roar and the calamitous whoosh of buildings exploding or collapsing. Great plumes of smoke arose into the sky; a condensation effect took place in the summer air and soon radioactive rain began falling on the pulverized metropolis.

On the ground, fire storms raged unchecked through the twisted ruins and whipped up ferocious winds that turned remnants of neighborhoods into kindling.

The people of Hiroshima had no idea what had happened. (In fact, the Tokyo government itself was left utterly in the dark until Truman's announcement 16 hours later.) Thousands were disoriented, bleeding, vomiting, dying. Some had burned skin falling off their bodies like pieces of charred clothing. And yet, there was no place for the injured and dying to go. All medical facilities were instantly overwhelmed.

The immediate toll of the Hiroshima bombing: 66,000 dead; 69,000 injured. The number of dead grew in the following years as people developed diseases and other maladies connected to the explosion.

A 1946 report by the Manhattan Engineer District called the atomic bomb "the greatest scientific achievement in history." There is no question it was an epochal, transcending achievement; only history can judge its ultimate merits.

In 1999, a panel of historians named the Hiroshima bombing the top news story of the 20th Century.