All 79 volumes of the official Army history of World War II are now available through one big fat link. I could waste weeks on this site.
Yes, I confess: I fear we focus too much on World War II in general. I once vowed to stop reading about World War II and the Civil War until I knew more about other wars, especially in other countries.
But how can you resist this stuff? You can't go wrong reading the specialized volumes here for valuable background on virtually any aspect of how a big military operates in wartime. There is, for example, an entire volume on U.S. military operations in the Middle East, and four times that many on military medicine in World War II. How many books have you read about military medicine in combat conditions?
Bonus: Here is Adm. Chester Nimitz's operational diary for World War II, now online.
U.S. Army Center of Military History