What was the atomic bomb's purpose in World War 2?

Answer 1

When the Manhattan Project was first started in 1942 with the goal of building atomic bombs the purpose of the new weapon was as a defense against the possible Nazi use of the atomic bomb that it was believed they had already been working on since 1939 and were likely to soon have in their arsenal. It was expected that following the German attack on the USSR in 1941 that the first Nazi use of atomic bombs (once they began building them) could be on either Great Britain or the USSR and that such an attack would result in a quick collapse and surrender of the country attacked with them. This would result in the US fighting the war against both Germany and Japan alone with only the oceans to delay the eventual attack by Germany on the US with atomic bombs (or having to surrender to Hitler's threats of their use without resistance in a futile attempt to "save American lives"). At least if the US had atomic bombs we might have some chance of fighting back against a Nazi atomic bomb used on us.

However by the time the Manhattan Project had actually succeeded in building atomic bombs in the summer of 1945 Germany had already surrendered and all the original assumptions of the project had fortunately been proved invalid. However there was still the war with Japan, which although it was obvious to everyone on both side that Japan must eventually surrender the war was moving slowly and with Kamikaze attacks and when entire Japanese units had to be killed to the last man as they would not surrender even when obviously defeated. If this continued the Japanese "D-Day" invasion would clearly have very very high casualties on both sides before the Japanese would actually surender. So the atomic bomb was now given the new purpose of an offensive weapon to shorten the war with Japan (and hopefully save lives).