I once found hour by hour reports on the battles of Guadalcanal and Peleliu. I can't find them to link to them and am on mobile, but if anybody knows of anything similar to this (and not just American. Any and every point of view is welcome) I'd love to see more.
Edit: I mean like the ones found at http://www.peleliu1944.com/aar.html
You can find submarine mission reports online and on Amazon. These are the reports that the captains wrote at the end of each mission and submitted to SubCom. They go into pretty deep detail.
US National Archives is one source, but you have to travel on site and learn where they were kept. I research Naval records and there isn't a single, sole repository of reports. The Archives holds records as they were turned over to them, so some might be in the Commander of the Pacific Fleet, while others might be in Army records. A more cost/time effective way might be a subscription to sites such as Fold3 which have already scanned in a lot of reports and made them online to subscribers. I think it's more fun to go there, personally, but it costs me about a grand a trip in airfare and hotel, so a Fold3 account costs a lot less.