For domestic bases, the delivery address is simply the street address as well as the city, state, and ZIP Code or ZIP+4 Code, (including P.O. box or unit number if needed).
For overseas bases, it becomes a bit more complicated. First, you’ll need to identify whether the Post Office is an APO (Army Post Office), FPO (Fleet Post Office) or DPO (Diplomatic Post Office). APOs correspond to any Army installation and FPOs serve the U.S. Navy and any carrier ships. DPOs apply to diplomatic installations, like an embassy.