I saw this posted on another website. Biblioteca Militare is online collection of various books and journals, many of which were published by the USSME. It doesn't allow downloading as a visitor, but you can read the items online. You can sign-up (I have not), but I don't know if that gives you any greater access/options. On the site are some of the USSME official histories, Rivista Militare, and more books and journals. I have not look at everything they offer (over 2K publications), so there is likely something for everyone.