There are 3 strategic moves I like to make in the soviet far east, and it works well do deter japanese intervention as well as stop gap it if an invasion occurs.
1. Re-deploy
Move the bulk of the Soviet units back to the saftey of Buryatia, leaving only single infantry in the other Soviet territories. Leaving single infantry in territories deters “land grabbing” with single Japanese units.
2. Re-enforce
Send a Fighter, Tank, and AA gun to the far east as soon as possilbe to meet up with the stack in Buryatia, or meet witht the stack as it is falling back.
3. Re-establish the Railroad
Because there is no way to quickly get troops to the far east, the only option is to funnel them eastward. A neat tactic is to establish a land shuck of Infantry to Buryatia. Move one (or two if you feel daring) to the east each turn. And also bleed off one from the stack to go west to establish the link quicker.
The link is established on R3, and even though you took 3 from the stack (or 6) you have now established a quick link to the east. Each turn Japan isnt killing Soviets, you can place one more on the border (or two if you did the gutsy move)
Even if Germany is hammering you it is still important to not ignore the the eastern front……those units will never get there in time to help you…they are best kept over there. And the money you save defending it will help the USSR have more troops in the west in the long run.
If you hold all the far east, and are only sending over 3-6 IPCs worth of units, you are gaining a guy in the west. Or a tank in the west if you are only sending single infantry eastward
Hopefully this strategy becomes adopted by more than just myself and we see a lot less Japanese iterference in the Soviet Far East