I'd have to vote for the Iowa-class BBs. Specifically the USS Missouri, BB-63, as it was on her decks that World War II finally came to an end with the signing of the unconditional surrender of Imperial Japan.
You can well understand why the USS New Jersey's firepower was feared by the Vietcong. The following description about the 16-inch main gun was given by a naval gunnery officer aboard the USS Missouri during the First Gulf War in 1991:
"Try to imagine an old Volkswagen hurtling through the air at over 2,000 m.p.h. and travelling a distance of 22 miles before smashing into your house."
Now THAT is one helluva gun!