I love building model ships so naturally I've seen some submarine model kits out there too. But all of them seem to only consist of the submarine's exterior. Basically a long bullet-shaped object.
The outside of a submarine just isn't interesting enough to warrant me building it. It's the inside of a submarine that really is interesting to me. It must feel so claustrophobic. And dark. So give me a model kit that has an interior and I'll definitely build that.