Moment of Truth
Recruits (from all of the services) are briefed about the "Moment of Truth." This is the moment of time (usually at the final departure from MEPs to boot camp, or during boot camp inprocessing) where recruits can "come clean" about anything they lied about or failed to disclose in their enlistment documents. While disclosing this information may still result in a discharge (depending upon if the information makes one ineligible for enlistment), disclosing it during or before the "Moment of Truth" will usually preclude criminal prosecution (court-martial).
Here is an example of the statement of understanding that new recruits sign. While the below was extracted from U.S. Navy publications, similar statements are signed by new recruits entering ANY of the military services.
Signed upon entry into the Delayed Enlistment Program (DEP):
"I have been counseled concerning the NAVYS MOMENT OF TRUTH. I understand that after my active duty enlistment, if I disclose additional information that is not listed in my military record, I could be subject to a $10,000.000 fine and an involuntary discharge from the U.S. Navy. I have been advised to list all civil involvement (juvenile or adult); drug usage, prior service information; dependant information and medical status information, etc. I understand that I will be investigated by the FBI and the Defense Investigative Service, which will be checking into my background. Their concern is national security. The Navy wants to know if I can be trusted. No matter what anyone has told me; NO RECORDS THAT ARE SEALED, CLOSED, EXPUNGED, DISMISSED, OR GUARDED ARE KEPT FROM NATIONAL AGENCIES WHEN NATIONAL SECURITY IS AT STAKE."
Signed at the MEPs on the final day before shipping out to boot camp:
"I have read again the statement above concerning the MOMENT OF TRUTH. I fully understand that regardless of what anyone has told me not to mention, that I MUST REPORT any information I have not already told the Navy about. I also understand that revealing any additional information is for my protection to prevent any chances of fraudulent enlistment."