Gentlemen-
A good source for "hard data" in regard to the US Army during the period 1900-1918 are the "Annual Reports of the Secretary of War". These were published every year and cover the Army's activities of the prior fiscal year (which runs from July 1 to June 30). There's even information on recruiting, desertion, and even venereal disease.
The best part is that some are actually online and can be downloaded as pdf files. The reports on the Army's activities in the Philippines are especially interesting. There's a lot of data in there that I'm sure has not seen the light of day since it was written.
The only problem with the online ones is that it's pretty uneven- these annual reports were multi-volume works and not all the volumes for a specific year are scanned. Kind of a pain since I don't have access to a university library.
The online versions can be found here:
http://books.google.com/Just type in "annual reports of the Secretary of War"
Also, there's a lot of other interesting period books available for download such as the Charles King novels.