When I was 20 I got caught for underage drinking, and before I start sending my stuff out to the guard , and getting processed I would like to know if I should disclose this or not. All fines were paid, and I did my community service. The record has been expunged and sealed. So after they ask me about my traffic infractions, should I disclose this, or keep it to myself. I have paid for private background checks to be done 6 months after the expungement, and they did not find anything, however of course those were civilian, and not federal.
As others have mentioned, DEFNITELY disclose this frequently and often during the process.
During the security clearance investigation
s (don't forget...there isn't just one, and you'll have periodic reinvestigations for basic clearances, additional investigations for additional clearances during your career, etc) they'll talk to your friends, relatives, previous employers, etc. All it will take is for one of those people to say, "well, there was that one time he was underage drinking..."
They will be able to find out, and as soon as they do you will be on the defensive trying to explain why you didn't mention it.
Generally the military doesn't care about the actual infraction -- they are looking for BIG problems that could indicate that you are a risk for future problems. Saying you got busted underage once is not really a problem. "Hiding" it, even if that wasn't your intent, is a problem. See the difference?
I go overboard on these things, personally. There is obscure crap that I bring up every time I'm in a reinvestigation, just to make sure they know there are NO skeletons. Usually they look at their paperwork and say, "yeah, we know about that one..." and it's a non-issue.