First thing is to never pull all Russian units to Sakha R1 (or even partial), Japs can move everything they have to Amur J1 (you won’t be able to attack them w/1’s), and trap you there. You can’t retreat, the Japs can hit all your options from Amur. Your dead, leaving them a clear path across the north, with only the Mongolian Russians to protect you. This does make it a little tough for Jap though because they will be expending resources they need in the south & China, but it can be devastating for the allies.
I normally retreat all Russians back (6 inf to Yak, and 12 inf +AA to Bury). Next turn continue to retreat 6 inf from Yak towards Moscow, or they can move into China later if not needed at home (Sea Lion). I keep the 12 inf + AA in Bury for now.
The game we’re playing now the Japs have moved everything south (very little left near Japan). They built a naval base in Kwangsi (pretty typical) to threaten India (we blocked them w/dd), or to grab the DEI, Phil and threaten Anz (Japs have 5-6 loaded tpts). Seeing that Jap moved just about every thing south, as US I started moving fleet to the north. I have things spread out from Hawaii (small fleet), Wake (2 loaded carriers w/1ftr on Wake), and sz 16 (1bb, 2 cruisers, 2dd’s & 2 loaded tpts) all out of Jap range (for now). We are just starting turn #3, and the Russians (12 inf+AA) will be returning to Amur (out of Jap range as well). If Jap attacks J3 (think they will, or at least that looks like what the plan was), I can get the US troops safely to Amur (sz5), along with 5 aircraft (on/next to Wake). I could also move everything to sz6, depending on what Japan does. I’m sure he’ll protect the Jap home island somehow, but it should put a damper on his plans to the south. W/US troops and air in Amur protected w/12 Russian inf+AA guns it will be interesting to see what the Japs do. If they don’t protect Manchuria, I can take it w/US, then move the Russians in for defense (Turn order) keeping the Mongolian rule intact, BTW we have also saved a couple IPC’s w/China to add more troops to Manchu once liberated. Korea is also an option for US/Russia to stage there. I could also send the US air force towards Moscow (from Amur) to def against the German heavy Barbarossa leaving the 20+ ground units, 2AA guns and Chinese ftr in Manchu (if we get it) for Japan to deal with (if nothing else it should chew up some very limited Jap ground troops). If the Japs move back towards the home land, the Anz & UK are set-up to snipe Jap tpts etc…
Anyways I like to keep the bulk of the Russians in the east just to F*** w/Japan. I’ll leave it to my allies to help def Moscow (air power, or troops from India etc…), or start up a 2nd front to stall the Germans in a Barbarossa game. Those Russians can be used in China or in this case may end up saving India, or stalling the Japs by combo w/US & China.