[Gerald]

Originally Posted by UnderseaLcpl

If you want to get really technical about it, no submarine has ever had a deck gun. By the time the first true submarine craft were introduced (rather than submersible torpedo-boats) the practicality of the deck gun had long since vanished.

Anyway, I hope this site helps: http://pigboats.com/subs/deckguns/deckguns.html

According to them, the case could be made for the Holland having the first deck gun.

Nice link,