The president of the United States for most of World War II was Franklin D. Roosevelt, but upon his death in April 1945, Vice president Harry Truman took his place. Upon completion of the Manhattan project three months after the death of FDR, President Truman was faced with a decision of unprecedented gravity. The President had attained the power to end the war, but doing so would mean unleashing the most powerful weapon mankind had ever seen and would cause the death of thousands of civilians. U.S forces had occupied many of the islands surrounding Japan and were intensely fire bombing Japanese cities. The Japanese however had two million troops stationed on the mainland to defend against invasion, so the war was at a stalemate. The allied forces first demanded an unconditional surrender, promising destruction upon refusal, without revealing then development of a weapon of mass destruction. The Japanese denied the Allies' demand, not realizing the destructive power the U.S had just attained. Promptly after the Allies received their response, the bombs "Fat Man" and "Little Boy" were built and loaded onto a plane named the "Enola Gay" and were to be dropped on Japanese cities.