[quote=@POOHEAD189]
could I be a stow away that has the skills to fill the role as master gunner? 
[/quote]

I do not think so, since there would be an NPC master gunner in place, and something bad would have to happen to the master gunner NPC for your character to take control. But you can still take the role and be retroactively there from the start. Or do you have other ideas for a master gunner character?