While doing research for some writing I came accross the following site for USAAC, USAAF, and USAF histories:

Air Force Link - Other History Sites

Once at this site go to:
Air Force History Support Office

Then go to:
Our Books and Online Publications

Scroll down and click on Publications by title

All of these items are pdf files but many include images and other details of interest to anyone wishing more information about aircraft and campaigns of the Army Air Corps and Air Forces.

The link below will take you to a list of United States Marine Corps resources available as pdf files.

I hope these will be of use.
Marine Corps Publications - Historical