ORIGINAL: 76mm
A few comments about the Sov AI: first, it generally did a terrible job of pulling back and generally sat there until it was almost completely surrounded. Second, it made lots of idiotic attacks in which it would punch a hole in my lines, push several divisions two hexes ahead, and only leave one or two divisions holding the hex which it just took. So it was generally very easy to attack the penetration at the base, cut if off and isolate the deeper Sov units, after which they were dead. Many times I would be on the verge of encircling a bunch of Sov units, and units at the western edge of the impending pocket would be attacking to to the west instead of pulling back to the east.
I think overall the AI isn't that bad about moving units given the large map and the wide range of strategic/tactical decisions to be made each turn. It is better than a lot of other games. That said it can certainly use improvement.
One thing that might help is to program the use of cards and political points. It does not use them anywhere near as good as a human will.
Speaking from a Russian AI point of view (as I think most people play the Germans) the AI should get a minimum number of Political Points each turn, say 50 on easy, 75 on normal etc. and the cost of replacement cards should be capped at 3-4 times the starting cost.
The first thing that should be done is is to replace leaders with organization levels that will trigger penalties. Once all leader have been upgraded they if should default to the way it is now for replacing them.
It should play certain cards every turn if they have the points. It should always play the fortification card each turn. It should then play the infantry replacement card followed by the tank card. The Russian AI will need bodies. After that cards should be played in a more random fashion. After a certain date the card playing should default to the way it is now.
The Tilbisi supply center should be automatically built by a certain date. It could be randomized but it should be given to the AI as it will probably never have enough points to build it when it is needed.
If threatened Stavka should move for free.
It should not build any new units until it's stance changes or on a given date, say December.