From Kim Komando
Get official military records and medals
You can request service records, replacement medals, even discharge papers (the famous DD-214) from the National Archives. It’s free. You just need the person’s name, service branch and birth/death dates if you have them.
National Archive
Dig up old draft cards and enlistment records. It’s hard to beat Fold3 (offers a free seven-day trial). It has a massive military record collection, including digitized WWII draft cards like the one I found.
Fold 3
You could also try FamilySearch (totally free).
Family Search