Remarkably the Project cost only nine days' worth of Federal spending of the period, such was the scale of the country's wartime mobilisation. In the event, the bomb wasn't needed against Germany, but could the US take the risk of foregoing its development?

Would US jets have changed the outcome? Germany's various projects didn't, and even with a major US development effort it seems unlikely that successful fighters would have entered service in large numbers before aerial superiority was achieved anyway.

The controversy surrounding the bomb's eventual use may make us question the desirability of its development, but the outcome wasn't so clear in 1942 or 1943 when a major diversion of effort into other weapons would have to have been initiated. But it's an interesting question. Might other avenues have been more useful? That inter-Allied bugbear of landing-craft springs to mind.