Why did the US atomic bomb program go further than the German atomic bomb program?

Answer 1

Largely because the German scientists on the Nazi project made mistakes that the US, British, and Canadian scientists on the US project did not make. Some of this was likely due to the German system of not challenging authority that did not exist in the US, Great Britain, or Canada. There is also some speculation that Werner Heisenberg (the director of the Nazi project) was more interested in provide work for German scientists that could keep them out of the German military during the war than he was in actually building an atomic bomb, so he may not have double checked things.

Some of the mistakes that the German scientists made were:

• when the German scientists tested graphite as a possible neutron moderator for use in reactors they found it absorbed too many neutrons to be usable and abandoned it, when the US scientists did the same they realized that the neutrons were being absorbed by boron contaminating the graphite and ordered boron free graphite for use in reactors
• the German scientists then selected heavy water as the neutron moderator for use in reactors, but there was only one plant in the world at that time capable of making the quantities of heavy water they needed, it was in Norway and the costs of making heavy water was many times that of making the boron free graphite that the US scientists were using
• the German scientists made an error in the calculation of the critical mass of uranium-235 that suggested that an atomic bomb would weigh about 50 tons, far too heavy for any bomber any country might be able to build before the end of World War 2, the US scientists correctly calculated the critical masses of both uranium-235 and plutonium and were able to build atomic bombs weighing 5 tons using both materials and had the new B-29 that could carry a bomb that heavy (the British already had the Avro Lancaster bomber that could carry a bomb weighing 6 tons, but the US wanted to use their own bomber not a British one)
• there are indications that the German scientists never discovered plutonium (which has a lower critical mass than uranium-235) which the US scientists did and found to be less expensive to make in large quantities using reactors than uranium-235 is to enrich from natural uranium (this oversight likely happened as Germany did not have large high power cyclotrons like existed at UC Berkeley where US scientists produced the first measurable quantities of plutonium in the world)
• etc.

These errors lead Albert Speer to have Heisenberg scale back their project, canceling all atomic bomb development and concentrating entirely on basic research on nuclear reactors that might be scaled up after Nazi Germany won the war to build nuclear power plants for generating electricity and probably inexpensive steam heat for nearby homes and businesses.