Consider using
www.familysearch.org as a starting point. It is free and has excellent tree building, sources and other tools. You can use it as a "front end" search engine for Fold3 and the National Archives. Also it might help you locate other useful sources which are not strictly military related. For example for one of my civil war relatives I located a state historical marker which mentioned him. The ability to link your ancestor to existing trees can help you find other sources.
Fold3 an Ancestry are fee services, but most municipal
libraries offer a free portal You can access the Fold3 or Ancestry data from your home computer using the library portal web site and your library card. When using the free library portal there are some restrictions, such as you can only download one page at at time, not an entire document. So to download a five page document you would have five separate pdf files, not one.
Cheers