Corpman, back on the river voyage I looked at where the N2 servicing connection is located. There are on tanks any longer nor connection fittings. I am goinging out on a limb and guess it was for purging the gun director and the electro-mechanical controlers on the 40mm guns. I have read where moisture was a problem with these systems. As for purging ballast tanks that would take a lot of CFM's to to keep purged.