Bud's explanation of the deck numbering system was in error. The uppermost full deck on a ship is the main deck. Going down, the decks are numbered 2, 3, 4, etc, with 2nd deck being the next deck below the main deck. Going up, the decks are number 01, 02, 03, etc., and are pronounced oh-one, oh-two, oh-three. They are called levels. On a carrier, although the flight deck is the uppermost full deck, it is the hangar deck that is the main deck. The flight deck is at the 04 level. The levels continue up through the island to approximately the oh-eleven level. The navigation bridge, where the Captain's chair is, is at the oh-seven level.
A gun that has been sitting on the bottom of a harbor for two days would not still have fingerprints on it, sitting in water, especially salt water, for that long would wash any skin oil residue away.