Why did president truman hesitate to use the atomic bomb?

President Truman at the time, had no idea of the extent of the effects of the Atomic Bomb despite being tested. The only reason he allowed it is because of having information that it was a "military base" and that no civilians would be harmed. Sadly this wasn't the case as Japan found out the hard way. Lastly, the Atomic Bomb costed 2 billions dollars at the time, and that would be a huge blow to the economy.

Ship building industry , good luck : )