I had the good fortune today to visit the Marshall Museum in Overloon, Netherlands with my son. Not a great deal of armor, but hundreds of other military vehicles, mostly US, and all in excellent condition. Thought I'd share our favorite with you. Unfortunately, I was a little rushed and didn't get its nomenclature, but I've never seen anything like it. Sorry for the dark pics, my camera flash is weak -
My 6-yr old is standing in front for scale. Under the body (hull?) in the second pic to the right of my son are the two tunnels for the propellers. I think the placard said these things were from the 1960s and were used in Vietnam. The open covers line both sides and house the engines.