If you have his service number (or even his date of birth and SSN), and if he is deceased, you can usually get the records through military archives. Contact the branch he served in, and ask for the Public Affairs or Public Information office, and ask what the current procedure is for those requests.
One piece of sad information - several years ago, there was a fire where these precious records were stored. Several years of documents were lost. The only way to find out whether your dad's records are still intact would be to place the request above. Good luck! I hope you can get that information!