YOKOSUKA NAVAL BASE, Japan — All mail sent to Navy ships, squadrons and mobile units must now use nine-digit zip codes or it will be returned to sender, according to a Navy statement Tuesday.

Mail without the nine-digit zip code that is currently en route will also be returned as undeliverable, according to both Tuesday’s statement and a July 12 service memo from Navy Secretary Ray Mabus.

The U.S. Post Office shuttered two of its coastal military mail operations and instead opened one processing center in Chicago, according to the statement. When they did so, they changed from manual sorting to an automated operation requiring the longer zip codes, which include the commonly known five digits, separated by a dash from the lesser known “plus-4” digits.

Commanding officers have been directed to provide sailors with their nine-digit zip codes so they can, in turn, inform their correspondents.

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