Just looking at the pictures of the "Lun" gives me an instant hard-on. That thing is just incomprehensibly cool in its brutality and straightforwardness. That monster looks like it was built by the Imperium in the year 40,000 but then fell through the Warp to our time
Why, oh why there are not much much more masterpieces of technological insanity like this in the world?
Though, thinking about its purpose, I would say that besides invading the US (or Sweden, or Denmark, or Iceland, or Greenland, or the UK, or Turkey, or Japan) from the sea, the Ekranoplans would have had another potential use as well, hence the SS-N-22 launchers (a ramjet-powered cruise missile is also teh win, btw) and sophisticated radars.
Namely, hunting down US carrier task forces and supply convoys in the Atlantic. While the SOSUS line extended from Greenland to UK via Iceland, submarines were not a practical option, unless one was willing to accept loss rates that would have made even Dönitz hesitate. (Capturing Iceland and Greenland would have made this easier - where the "Lun" might have come in handy too, but let's assume that would have been too difficult to pull off.) So an airstrike was the tool of choice. A strike force consisting of regular bombers - Tu-95 Bears, Tu-16 Badgers, Tu-22 Blinders, Tu-22M Backfires - would have had to fly high in order to have the range to reach mid-Atlantic. And flying high they would have been detected much more earlier and easier (well above horizon, no ground clutter to hide in). And there was the additional risk that they could have been detected and intercepted coming and going through the Iceland-UK gap. Assuming that there had been an extended-range variant of the Lun (the Wiki entry states a range of only a couple of thousand of kilometers for it, even though ekranoplans are supposed to be more fuel-efficient than regular aircraft), it could have easily passed through below radar. As a ground effect airplane, it would not have had any difficulties staying at wave height, unlike regular aircraft - and combined with high-speed missiles, would have made defending agaist them nigh-impossible. The only tricky phase of the mission would have been locating the American carriers and convoys (the Lun had its own radars, but radar horizon works both ways), but if the missions were timed to hit mid-Atlantic when a recon satellite made an overhead pass, that would have been probably enough for preliminary target designation.
Well, there's also the third option besides troop carrying and anti-shipping duties. The Sunburn (if other missiles were not fitted) could also accept a 120 kt thermonuclear warhead. So the "Lun" would also have been the perfect tool for a decapitating first strike. Makes the fictional "Red October" look archaic in comparison. Why use something as slow and vulnerable as a submarine, when you could use a sexy beast like this?
