A fleet post office or FPO, a branch of a civilian post office of the U.S. Postal System, operates under the Department of Defense and serves personnel serving in U.S. Navy installations and ships.
FPO Mail Handling
Because FPO mail bears either a U.S. military destination or return address, the Department of Defense handles it at some point of its delivery.
FPO mail can either originate from or be sent to addresses outside the U.S., and includes both personal and official communications.
FPO mail undergoes processing at centralized facilities in New York and San Francisco. Letters arrive in sleeved half trays, flats in sleeved plastic flat tubs, and parcels in sacks.
FPOs have ZIP code numbers similar to those of their respective U.S. cities. This allows the U.S. Postal Service sorting machines to correctly process FPO mail.
After the USPS sorts FPO mail addressed to overseas destinations, the Navy delivers it to its personnel at FPOs similar to civilian post offices that place the mail into a lock box for each address holder.