President Harry Truman never expressed doubt about his decision to drop two atomic bombs.

"To us, it may be a horrible weapon," said Barton Bernstein, a Stanford history professor who has studied Truman's actions. "But to him it was a powerful weapon to be used against a hated enemy in a just war."

Historians say - given the terrible losses expected from invading Japan, the Manhattan Project's $2 billion cost and the desire to convince the Soviets of the United States' superiority -the only surprise would have been if Truman hadn't decided to use the bomb.

"Back in mid-1945, there would have been no reason for an American leader not to have used the bomb," Bernstein said, though he believes the Nagasaki attack was unnecessary.

Blanket approval to drop as many bombs as available was given in a July 25, 1945, order to Carl Spaatz, the head of the Army Strategic Air Force, by Thomas Handy, the acting chief of staff.

The targets were Hiroshima, Kokura, Niigata and Nagasaki.

Another atomic bomb would have been ready by mid-August. Plans called for three more bombs to be ready in September, and as many as seven by December.

But after the Nagasaki raid, Truman ordered no more nuclear attacks without his explicit approval. He was tired of killing, particularly "all those kids."

"The final decision of where and when to use the atomic bomb was up to me," Truman said in his memoirs. "Let there be no mistake about it. I regarded the bomb as a military weapon and never had any doubt it should be used.

"In deciding to use this bomb, I wanted to make sure that it would be used as a weapon of war in the manner prescribed by the laws of war. That meant I wanted it dropped on a military target ..."

Most of Truman's advisers supported dropping the bombs, though there were exceptions. At one point during the Potsdam conference in Germany, Truman ate lunch with Gens. Dwight Eisenhower and Omar Bradley.

Though Truman didn't ask either about using the bomb, Eisenhower indicated he was opposed to using it because he thought Japan had already lost the war, Truman biographer David McCullough wrote. Earlier, Eisenhower told other top U.S. officials the weapon was so horrible he hoped the United States would not be the first to use it.

Truman clearly understood the bomb's destructive power.

"We have discovered the most terrible bomb in the history of the world," he wrote in his diary July 25.

"It is certainly a good thing for the world that Hitler's crowd or Stalin's did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made useful."

When the first atomic bomb was dropped on Hiroshima, Truman was returning to the United States from Potsdam aboard the USS Augusta.

"He was not actually laughing, but there was a broad smile on his face," United Press reporter Merriman Smith said of Truman's expression as he announced the bombing to crew members.

Three days later, Truman was back in the White House when the Nagasaki bomb was dropped.