The use of atomic weapons forced the Japanese to surrender. Many argue that the bombings were unnecessary, stating that more conventional methods may have been as effective. Casualty estimates for an invasion of mainland Japan were in the hundreds of thousands on both sides, so President Truman believed he was saving lives. Some say dropping the atom bomb was his only option. If the public learned that the President had a weapon that could end the war in 1945, but chose not to use it, the court of public opinion might have judged him as weak and incompetent. President Truman would bear the weight of that decision for the rest of his life, "I made the only decision I ever knew how to make. I did what I thought was right."