As ct mentioned, the U-505 was captured during WWII and someone figured out how to drag it to the Museum of S&I. I took that tour circa age 12, and was struck at the amount of valves and gauges and of course how cramped the thing was. Those were formidable weapons, and had the WWI uboats not been so effective, the Third Reich might have had more of a surface navy. Not sure, but I believe the naval Enigma machine on display at the Air and Space museum (go figure) in DC came from the U-505. The A&S museum display is the only place in the world where both the army and naval versions of Enigma can be seen. Not too sure there are many displays of either one, anyway.
Thanks for this article, SC!
Love living in this age when the sea is giving up so many of its secrets.
For those also interested in WW2 German U-505:
http://www.msichicago.org/whats-here/exhibits/u-505/
Here is a German U-Boat passing under the Brooklyn Bridge:

Being hauled out of Lake Michigan:

They dragged it accross Lake Shore Drive to the Museum:

It felt cramped with a tour group of about a dozen. I can't imagine being in that thing fully provisioned for a war cruise with a full crew.
There is an Enigma in the Imperial War Museum in London, but I can't remember now if they had one or both types.