I think I'm missing something on the supply rules - I was hoping someone would be able to help me out.
I've read a couple posts suggesting that a Soviet Spain can be a powerful option. However, if the USSR successfully gets Spain as a Satellite, wouldn't it be trivially easy for an Enemy to put Spain out of supply (by cutting off the Med/North Sea)?
You could stack the country with ANS units to avoid the OOS penalty for ground units, but you still wouldn't be able to buy a unit step for them while they were unsupplied (7.23). So wouldn't a Soviet Spain quickly become isolated and conquered? More generally, does it make sense to focus your diplomacy on countries that are adjacent to you?
Easiest way is probably German sub in the Norwegian (or Barents, I think) Sea, conquest of Denmark, and an Italian unit somewhere in the Med (conquest of Malta could do it). The big problem I see for the Soviets is that if that blockade IS established, they may have to rely on the West to break it, and depending on cards selected that may not even be possible.
Though you can place AF, naval assets and forts there, which can be a nuisance to whoever oppose you.
Ships especially can hinder West naval movements toward India in case that is in the Soviet plans.
On the other hand, meanwhile Spain is interesting, a Soviet can also weight how much good can do i nthe hands of the Axis (luring them to pincher Paris) and shifting Axis focus West. Always depending on Soviet projects.