Which authority grants waivers to prevent a service member from being separated for a second alcohol-related incident?

The authority that grants waivers to prevent a service member from being separated for a second alcohol-related incident is the Naval Personnel Command. This command is responsible for managing personnel issues, including disciplinary matters related to alcohol incidents. Specifically, established policies dictate that in circumstances where a service member has faced repercussions for alcohol-related offenses, they can apply for a waiver through this command.

The other choices, while they hold significant authority within the Navy and Marine Corps, do not typically handle the specific case of waivers related to alcohol-related incidents at the same level as the Naval Personnel Command. The Chief of Naval Operations and the Secretary of the Navy have overarching responsibilities regarding Navy policy and direction but do not get involved in individual personnel waiver requests. The Marine Corps Command, while relevant to Marine personnel, does not have jurisdiction over Navy personnel matters. Thus, Naval Personnel Command is the most appropriate authority for this specific situation.