Answer:

uss

Answer	Crossword Clue
USS	Battleship letters
USS	Constitution preceder
USS	"Enterprise" letters

USS	Destroyer letters
USS	... Ronald Reagan
USS	American vessel's letters
USS	Vessel insignia
USS	Constitution abbr.
USS	Enterprise letter
USS	"Arizona" letters
USS	"Constitution" inits.

USS	Naval letters
USS	Ship letters
USS	Broadside initials
USS	... Constitution (historic frigate)
USS	... Monitor (Civil War ironclad)
USS	...Constitution, nicknamed "Old Ironsides"
USS	Navy-vessel letters
USS	Liner letters

USS	Naval initials
USS	Seagoing letters
USS	Battleship initials
USS	Capt. Kirk's .. Enterprise
USS	Constitution beginning?
USS	Fleet letters
USS	.. Ronald Reagan
USS	Battleship inits.

USS	Sub letters
USS	.. Enterprise
USS	Amer. ship designation
USS	Letters at sea
USS	Naval cruiser letters
USS	.. Constitution
USS	.. Nautilus
USS	Navy ship letters

USS	Letters on the Ronald Reagan
USS	Nimitz letters
USS	Carrier letters
USS	.. Intrepid
USS	.. Arizona