The research tree is sometimes somewhat unclear and I can't easily find all the tech needed for vehicles and ships, and is there no way to modify planes in more detail than just adding the numbers for engine, armor and the like?

1. Where do I find the tech for DP guns for ships?
2. Why can't you add specific detailed research addons for planes rather than numerical values?
3. Is there any radio for tanks and if so, where in research?