I just got back from the National Archive, and found it amazingly easy to find my ancestor. Went through a microfilm of file cards relating to pension files; identified him by the name of his widow and minor child. Using the file numbers from that card pulled his file and two hours later I had the original documents in my hand! I know there's a lot of info on line, but because my ancestor's name was common, and I didn't know which unit he served in, I couldn't identify him by the online sources. The staff there was very helpful and knowledgeable. Good luck in your search.