Happy new year 2019!
Here is a quick and dirty remix of bolbots Seehund (Thing 3252705). I'm planing to place this on my model railroad clubs HO scale layout as a prank. Just to see how long it takes before it is noticed. Similar to the Sasquatches that have appeared in the logging section of the layout, or the Dr. Who Daleks and Tardis that appeared near an industrial siding (K9 was just too small to print with my fdm printer unfortunately).
A piece of wire can be fashioned into a periscope to finish this model. A paint similar to Testors 1740 Dark Gull Grey FS 36231 should work for overall colour. With a bit of dry brushing and some rust and grime wash it should be reasonable.
I claim no ownership of the artwork for this model nor its accuracy. I have not printed this as of yet but have checked it with microsoft's 3d builder for any flaws. So it should print without too many issues.
Good luck and have fun! If you print this and please post a picture.