Aircraft armament is an area of firearms study that is vastly under appreciated by most people, largely because it's difficult to study aircraft guns without the aircraft themselves (and those take up a lot of storage space, among other things). William Wolf's book on US WWII aircraft armament is actually much more than the title would suggest, basically covering all aircraft gun development from WW1 through 1945 (and later, in some areas). In addition, he discusses in dense detail the surrounding equipment that is a critical part of these guns: turrets, gunsights, ammunition, early radar systems, and more.

This is a book that will give you a tremendous crash course in all things aerial gunnery related. It is virtually all data, with little fluff at all (although there is some analysis, like the section on the debate between cannon (slow but very destructive) and machine guns (faster but less impactful). It's not a book I would expect anyone to read cover to cover, but rather it is there for reference, or for reading sections individually for a bit of daily learning.

While the technical sections on things like electronic fire control systems will put some people to sleep, I think the balance between that and the firearms themselves is well done. The sections on iterative developmental models of all sorts of US aircraft guns are very interesting (and it includes a wonderfully snarky John Browning quote). The cover price is $70, and for the information it includes it would be a bargain at twice the price. If you have any interest in machine guns or firearms mechanics, it's a great reference on a very much under-recognized aspect of the subject.