Specifically, what money was put into the various research depts. of each country, what was actually invented, the political intricacies.
In essence, are there any reputable books about the Allied and/or Axis effort of R&D in any field (nuclear, agricultural, small arms weapons, so on)?
Thank you for reading (in both senses of the word ;) )
David Edgerton's two books 'Warfare state' and 'Britain's War Machine' are nice readable books. The first is more academic than the second (war machine is definitely aimed at a popular audience). Both are interested in wider British institutional approaches to funding, procuring and developing war materials. Both look at efforts of public and private science, R&D etc. How science and engineering aspects are represented in military/governing circles etc.
Might not be what you are looking for, but both are quite readable. Warfare state poses some quite interesting revision to older 'declinist' views of British funding, innovation and adoption in the military industrial complex.
For the US you can use Stewart's Organizing Scientific Research for War (1948) for an overview of the Office of Scientific Research and Development's activities and spending. It does not include in-house military research.