Crikey, they're early ones. I was vaguely aware of this overland business but would love to see how they did it...I'm thinking trucks here! Here's a little bit from Uboat.net: uboat.net - The U-boat War in Maps - The Black Sea I was "so close" in October 2005! LOL.
Andy In case you couldn't get into the link, here is the picture of the truck. Can't see the trailer very well but it must have had a lot of wheels. (Even stripped out of all equipment and probably the engines, they must have weighed several hundred tons). And U23 was once commanded by Otto Kretschmer. And, the final skipper of U20, just 21 years old at the time, is apparently still alive - can't be many WW2 U-boat skippers still around.
Thanks AR, what an amazing pic. I meant to follow the link but got distracted. Excellent series of photos.