The United States need to maximise the effectiveness of its atomic weaponry program before it could be compromised  There was no possibility of keeping nuclear weapons under wraps; scientists from several countries had been working on them. They were ripe for discovery. Robert Oppenheimer pointed out “it is a profound and necessary truth, that deep things in science are not found because they are useful; they are found because it was possible to find them” [1] If Atomic bombs were going to be developed anyway there was a compelling reason to be the first to own these weapons, even to be the first to use them. Deterrence, would not work if suspected to be a bluff or a dud, having used the bomb twice it could not be doubted that the US was willing to use it again in extremis.  The cost of building the bomb was enormous. At 2.2 billion dollars the Manhattan project cost about the same as the drive to get to the moon in the sixties, but the comparison is not adjusted for inflation. [2] The vast majority of the cost, and of the 130,000 employed in the project, was not in the development but in the building of the factories to produce the fissile material. The opportunity cost of that 2.2 billion is surely huge, how many more bombers and tanks or how many more medicines and bandages could it have bought? Not using the bomb and squandering that investment would bring that opportunity cost to life; the question is not just how many would die in months more war but how many might not have to build something unused.  [ 1 Robert Oppenheimer quoted by Richard Rhodes, ‘The Atomic Bomb in the Second World War’ in C. C. Kelley (ed.), Remembering the Manhattan Project : Perspectives on the Making of the Atomic Bomb and Its Legacy, (River Edge NJ, 2005), p.18  [2] ibid p.22