Depending on the period someone is looking for, there are a large number of references in my military data thread.
http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=29049
Then there is the Center for Military History website.
http://www.history.army.mil/index.html
Aside from the official history of the US Army in World War 2, there is also the history series for previous American Wars, as well as the Korean War, the Vietnam War, the wars in Iraq, and the war in AFghanistan.
Then this is the Combined Arms Research Library Digital Library, where vast amounts of information can be downloaded.
http://cgsc.cdmhost.com/cdm/
The Combat Studies Institute website also has a large number of downloadable books.
http://cgsc.cdmhost.com/cdm/landingpage/collection/p16040coll3
For our Australian members, there is the Australian office histories website, with downloads.
https://www.awm.gov.au/histories/
Then there is HyperWar, World War 2 on the web.
http://ibiblio.org/hyperwar/
Then there is the Marine Corps history website, again covering from the Revolution to Iraq and Afghanistan.
https://www.mcu.usmc.mil/historydivision/Pages/Staff/Publications.aspx#2001
There is the Air Force Historical Research Agency website.
http://www.afhra.af.mil/studies/index.asp
And the US Air Force Historical Support Division website, covering Air Force history up to the present.
http://newpreview.afnews.af.mil/afhso/booksandpublications/titleindex.asp
Downloads are all available from those websites at no cost, and pretty much all documents are in the public domain.
Also, I am perfectly happy to answer any questions regarding reference books in hard copy, as I do have an extensive library on military history covering from the Sumerians to the present. This does include reference material covering logistics and weapons effects.
What all are people interested in?
Presently, I am teaching my class on World War 2, and we are analyzing the decisions made and not made at the Arcadia Conference in Washington, D. C. in December of 1941 through January of 1942.