The key was well protected by some scurvy-dog pirates and their assortment of booby traps, but I made it through their lines to the the chest. There was no fear of aerial bombardment today, but I heard ground forces all around me -- never made any visual contact, though.
After securing the key, I began to head back for the extraction point. I was not followed by any of the pirates (they must have taken too much grog trying to stay warm to have had any notice of me), and I don't think that anyone else followed me either.
I know that I only have half of the information I need, but half is better than none. I will post the required picture soon -- I don't think "they" monitor this channel of communications. I am watching my back though -- "they" must want this treasure as much as I do.