After I wrote the last post, my cousin, who's presently in Jersey in the UK, wrote and gave me a couple of links to videos of the Ekranoplan KM Caspian Sea Monster. I'd never heard of this seaplane before. It's not a pretty-looking thing, I must say; quite clunky, in fact. And it seems....large - a real monster. The comments on the first video provide some background, although, like so many comments on You Tube, it's hard to pick which commenters actually know something and which are just guessing their way through.
The video below is about 11 minutes - and the commentary is in Russian, so you have to guess what's being said about it. There's an intriguing moment about six minutes in when the thing lands on the sea then slides up onto the sand.