It doesn't matter if it is expunged or not... They WILL run your fingerprints at MEPS, so even if you had it expunged (and subsequently did not list the charge), it will show up on your NACLAC check. They just send your digital fingerprints to the FBI, and your "rap sheet" will be waiting for you before you ship out.
This is why the question is worded: "Have you ever been arrested, charged, cited, held, or convicted of ANY law violation (to include juvenile charges) by ANY law enforcement agency (to include Military Police, Dept of Natural Recources, Fish and Game Wardens, Juvenile Authorities, etc), even if the charges were dropped, dismissed, expunged, sealed from the record, or you were later found not guilty (do not list any charges previously listed)? This includes minor traffic charges."
Provided the charges were actually dismissed (not pre-trial intervention, first time offender or other diversion programs), you have a shot at the clearance. By not listing the charge, you will be discharged from the Delayed Entry Program, and barred from enlistment for 2 years. You will then require a waiver for the fradulent enlistment after the 2 years have passed.
Since you are inquiring about expungement, I am willing to bet on some sort of PTI in the case... Otherwise known as an OAD by the military (Other Adverse Disposition), and you are presumed guilty for waiver and security clearance purposes. The charges were never "dismissed," but adjudication was withheld.
Although I am not affiliated with the Navy in any way, feel free to ask me anything on the subject... I am an Army Recruiter, and I have a copy of AR 601-210 (Regular Army and Army Reserve Enlistment Program) by my side. This regulation defines the standards for enlistment in the US Army, and each service has their own equivalent (yes, they all say the same thing regarding OADs). You will require a waiver for enlistment as it is, so kiss the security clearance goodbye for now. If you fail to disclose the charge, I already told you what will happen.