It is neither one.
Since it's been a couple of days, and Alix got the closest, I'll declare Alix the winner. Post something up!
Here's what it is: This is a template that shows the actual hull diameter/size of the first submarine, the H. L. Hunley,
to successfully sink an enemy ship in combat, the U.S.S. Housatonic.
I was in Charleston for this past weekend and fulfilled a 6-year dream to visit the Warren Lasch Conservation Center on the old naval base and see the Hunley. She was discovered in 1970, but wasn't raised until 2000. All of the original crew members were still aboard, and many mysteries were solved, while many still are unsolved. Seeing this piece of history was one of the most important things to me that I hadn't done yet, so I was *very* excited. You aren't allowed to take pictures up on the catwalk around the boat, but suffice it to say I was awestruck.
Here's a shot of her after she was raised before she was transported to the WLCC.
And in the tank before the excavation: