Re the USS Alabama, they're probably just not looking for it at the moment, since there's nothing they could do with it right now if they located it. When they start seriously looking for it, I'm sure it will turn up quickly.
"Television footage also showed flooding as far east as the Florida coast.In Mobile Bay, it appeared that waters inundated buildings near the historic battleship USS Alabama, a tourist attraction docked on a causeway that crosses the broad bay. It was impossible to confirm the extent of the damage, however, as the reports were sketchy and contained no commentary."
http://www.gjsentinel.com/hp/content/shared/news/nation/stories/08/29katrina.html
It sounds like the water got high enough to break the ship lose.