While President Truman ultimately made the decision to drop the atomic bombs, the Manhattan Project and the development of those bombs was a decision made by President Franklin Roosevelt General Dwight D. Eisenhower Prime Minister Winston Churchill scientist Albert Einstein

President Franklin D. Roosevelt was the one who ultimately made the decision to initiate the Manhattan Project, which was the research and development project that produced the first nuclear weapons during World War II. The project began with a letter from physicist Albert Einstein to President Roosevelt, warning that Nazi Germany might be researching an atomic bomb and suggesting that the United States should do similar research. While Einstein played a pivotal role in alerting the United States to the potential of nuclear weapons, he was not involved in the decision-making or development process. General Dwight D. Eisenhower was a military leader during World War II but was not involved in the decision to begin the Manhattan Project. Prime Minister Winston Churchill of the United Kingdom was an ally and supportive of the project but did not have the authority to make decisions about American research projects.