The south is a much more complicated beast and depends heavily on the German opening to adapt to. Perhaps the most important factor to consider is that the railhead extends from Rumania (with a few exceptions given the weird rule that lowest MP distance is calculated first, and then the hex distance derived from it. This leads to situations NE of the Dnestr rough tiles where, although closer as the crow flies to Rumania, the hexes are closer by MP to Poland and thus give a very large hex distance). This means that the entire region west of Kiev is open game for German armor. The only "safe" retreats are towards the Pripyat marshes and towards Odessa, hopefully squeaking out by Nikolaev before the jaws shut close. Many players, myself included, tend to get pocketed in the Kishinev region. Besides the obvious negative part of losing troops which tend to be better than your other ones (turn 1 random morale/exp/TOE rules), a connection to Rumania there generates a slingshot effect whereby panzers are 10-15 hexes from the Rumania railhead and get pushed into Ukraine proper with good MPs.
The Soviet player simply does not have enough resources to prevent everything from happening, as the German is happy to play near Vinnitsa and double envelope Kishinev on turn 2. 11 and 14 Panzer can cross into Rumania to loop around from the south with likely full MP. In conjunction with the very low railcap, then, most of the units there are doomed if the German plays well. I've found four options in the south to either attempt to save those units or let their capture generate the most value.
1. Defend the rail hexes (assuming railing FBD 1 to Rumania, as we have here). Best case scenario, this delays the German two full turns of rail and occupies some of the German divisions and armor for a while. Worst case scenario, units are pushed off the rough tiles easily, and FBD 1 with Rumanian FBD have no trouble getting their 4 hexes converted per turn. This strategem assumes you will get pocketed absolutely, and it can be worthwhile to transfer the units to an army led by Zhukov for maximal CV.
2. Defend behind the Dnestr. This is perhaps the most common opening, but without sufficient blocking of the rail line from Vinnitsa to Odessa, Panzers easily swoop in and make the double envelopment. Now, it is possible with the two cavalry units near Odessa to threaten and opening here, and I will consider this, but I doubt Tyronec will repeat his leaks as in the BrianG game here.
3. Build up NE of Kishinev. This move denies the double envelopment (see 11P and 14P maximum ranges along with all panzers). However, the Germans will almost guarantee a Rumanian railhead the next turn and be able to pocket these units near Nikolaev.
4. Checkboard between Proskurov and Vinnitsa. Units are guaranteed to be lost here, perhaps all of them, but this delays the advancement into Ukraine.
Pripyat options:
1. Hug the marsh. This can be good play. If the Soviet dangles some juicy mech units not quite in the marsh, the German pretty much has to mount a Pavlovian response (that one would expect in the Western front instead!) to claim them. This puts them the armor away from Ukraine. This option is riskier due to the foray to Luminets. Cutting the rail north of Zhitomir dooms all of those units.
2. Strong defense in front of Zhitomir. Similar option, but will take more resources and hanging out in the area to clear the pocket. I have performed this pocket myself and have seen two others do it devolving into a brawl. A reasonable possibility given the German rail plan to delay armor.
3. Checkboard from marsh to Vinnitsa. Probably the most common plan and pretty much guarantees a surround. Panzers will be closer to Ukraine and railhead, so this is a the clear loser in my book.
Which choices I make will depend on my rail options, to be explored in further posts!
