Fifteen inches seems like a lot of inches when you're talking about hurling a projectile at people you want to kill in 1861, but not when you're talking about a human being spending time in something that wide. I just measured myself, and it seems extremely unlikely that I would have survived Hurricane Camille on Ship Island. Although with a little lube and some motivation, who knows? Interestingly, you can see the remains of three different coats of black paint at the bottom of this shot...looks like Rodman Gun painters are getting progressively less enthusiastic about getting down deep in there!