This is also fascinating:
Foreign Policy AT ForeignPolicy
The Russian army’s failure to capture important logistical hubs in Ukraine means they cannot commandeer local railway infrastructure to transport their infrastructure and soldiers farther into Ukraine and capture more territory.
Dr Phil Weir AT navalhistorian
AT ForeignPolicy piece by Emily Ferris of AT ISS_RUSI looking at Russia's reliance on & troubles with rail transport in its #UkraineWar However, it's worth bearing in mind, particularly amid further talk about Odesa & Mykolaiv, that Russia also has a port opening problem.
Probably the first port Russian forces took in the first days of the #UkraineWar was Berdyansk. The first ships to enter arrived in the middle of March & around ten days later they appeared to have cleared just two berths, whereupon the Saratov was sunk.
It would appear that since the loss of the Saratov, Berdyansk has either not, or been little used. Whether this is due to the sunken hulk of the Saratov & other damage, or ongoing issues with the port's security from further attack, or both, is unclear.
It now appears that Russian forces have taken control of the larger port area of Mariupol, which is known to be blocked with sunken cranes & other vessels, is almost certainly mined & has suffered far more extensive damage than Berdyansk.
By any stretch of the imagination, Mariupol will take an enormous amount of work to restore to anything resembling working order & it's unclear that the 68th Fleet Naval Engineers Regiment (Black Sea Fleet's engineering unit) have anything like the engineering capacity required.
In theory, possession of key ports like Mariupol & Odesa would allow Russian forces to at least start to unjam & bypass some of their worst logistical bottlenecks (though by no means all, of course - once ashore, material would still have to be distributed by road or rail).
Likewise, it should be added, transport via Ukraine's extensive inland waterways, particularly the Dnipro, also remain shut off
In short, the apparent state of play at the relatively small port that they have been in occupation of for some time does not bode well for Russian forces being able to exploit Ukraine's maritime south, even if they do manage to take possession of other key ports.