That's pretty impressive. I have a game (dormant for the moment), my 2nd as USSR, where I built level 10 forts behind the Dom, and up to just before Moscow & Leningrad. They discouraged many attacks (except that flat area just SW of Moscow), and I launched counter attacks in '44.My first attempt I tried to hold at the Dnieper & got crushed.
Well virtually all my games have been as the Soviets - one brief go at Germany 3-4 years back. Basically started with them as the easiest great power to play - no threat until ~June 41 in a single player game, only one front and no great naval needs. Being a bit of a micro-manager and having other commitments at times it generally means that by the time I get to about 43/44 and I'm somewhere on the Rhine there's a new mod of the game out and I have to think things through again. Plus initially I was blundering around, finding out assorted things. [For instance in my 1st game I assumed that having signed the pact with Germany, to occupy eastern Poland I actually invaded as historically and found myself at war with the western allies. Took a bit of time/digging to find out that you just get them automatically when Germany has conquered Poland.!] Had a family commitment for the past couple of years so have rather dropped out and now have another very addictive game keeping me busy.
Probably my best game had me conquering pretty much all the continent, including Iberia as when I attacked Vichy France Spain and Portugal joined the Axis - which at that point consisted of the Italian footholds in Africa and Corsica/Sardinia and the newly joined Vichy. Even got Gibraltar as a bonus as this meant Franco was also at war with the western allies and I presume Britain had left it ungarrisoned. This was an earlier version where Germany almost always conquered Britain and Italy overran much of Africa, fortunately that doesn't seem to happen as much now. Was going to try a longer game with a liberation of China and as much as I could of the rest of the Japanese empire then possibly see how I rated against the western powers but shortly after the liberation of Gibraltar the game just kept crashing!!
In my early games I used forts a lot but found them too easy as unless you strip the garrison to just about nothing even the AI gives up attacking and also it does tie up a fair bit of resources that are literally immobile. Hence don't use them at all nowadays.
My standard approach goes for roughly an historical game other than rejecting the purge, Hell of an effort burning off the resulting dissent but gives more military and also a couple of useful tech teams and most of all markedly higher organisation and morale. I do go for the conquest of Finland, which with the 1.10 version basically means holding the front line while having two amphibious assaults, one seizing Turku and then attacking Helskini from the west and the other going for Vaasa, while making sure not to occupy any other provinces.
Tend to occupy Latvia and Estonia in autumn 39, partly because it gives more time to use their production and partly because the diplomacy system is very limited for the Soviets so never had much confidence in it. [One early game I tried everything to keep Romania at least neutral, getting relations up to +200, rejecting the option of seizing Bessarabia, guaranteeing their borders and they still immediately joined the Axis when the Germans attacked], Hence I normally take Bessarabia as well as the hills of Chisinev and Beltsy generally form the southern anchor of my line. In the past I left Lithuania independent as the Germans never seem to attack or ally with it so it shortens the defensive line. However in that last game I did take it as well. My basic defensive front line was Chisinev, Beltsy, Stanislawow, Tarnopol, Rowne, Pinsk, Slonim, Grodno, Alytus, Siauliau and Jelegava IIRC which is slighly more forward of my normal line but gives only 11 provinces to defend, makes decent use of terrain and can only be attacked from two other provinces in most cases so preventing any multiple axis attack bonus. [I thought there wasn't any but notice that both Pinsk and Beltsy can be attacked from three provinces so could be remembering wrongly as the actual game is on my laptop.] Possibly I also successfully defended Ismail. Know I did lose one of those provinces in the north early, think it was Alytus which meant that Saiuliau could be attacked from three provinces and I feared that the north of the line would collapse but despite some bitter battles there the rest of the line held and by the late autumn the Germans were so blooded that I was holding the line fairly easily.
In terms of production/research and the like I tend to do a lot of infra and 10 lines of factories, although most of those are stopped once the non-purge dissent hits and generally only Moscow keeps producing during the 40-42 period while resources are at their tightest. As well as main production and resource centres I try to get the front defensive line and a link between it and Moscow as high infra as possible, largely to make reorging as efficient as I can. Sometimes change the Chief of Staff to one of the +20% Org regaining people to help here. Although I think in my last game I never got around to it and kept the +25% manpower man there.
I develop a broad range of production technology and prioritise Inf and related tech, i.e. AT and Art brigades. Normally seek to push for max war Hawk and drafted army - the latter partly historical and partly for the cheaper production, although I think standing army might be better in the longer run.
Early on, while I don't scrap any units and produce some transports and escorts for the amphibious attacks on Finland plus some motorised IIRC for that the only other units I produce are some either Cav or Gar/Pol to help in dissent suppression of the key production/resource areas when I reject the purge. Its about mid-late 40 when I get Inf 41 that I start mass producing INF 41 with either Art, in most cases, some AT and a few Eng brigades, along with reallocating some of the already existing ones. I also have two lines of Mtn divs with similar brigades as I like to stiffen the hills at the south of the line with a couple of Mtn armies. Also some motorised or mech - can't remember which - for quick response. Aim was to have ~140/150 Inf 41 divs about 24 Mtn and as many mobile units as I can. The latter usually with SP Art. Want an army of 9-12 brigaded Inf, one of which is a Eng for the level 40 entrenchment in each province of the defensive line with corps of other and of mobile units to reinforce where attacked. This means a lot of the line may be quiet as the Germans will only attack certain points but it gives security and also, if the supply is available I can provide artillery support by pounding the attackers to do some damage and reduce the infra of those provinces. Think I was some way short of this with only 9 Inf divs or possibly 6 in some places when the Germans attacked but managed to hold.
IIRC I hadn't built any new armour at this point as I simply didn't have the time/IC. This was my 1st game for a time and 1st with v1.10 so wasn't as find tuned as it could be. Also didn't really have any new air other than some INTs that I rarely used as they tended to get swamped and my ground troops were able to withstand the air attacks. [Had built a radar in most front line provinces and a number of AA which probably helped.
Anyway that was the gist of my plan, with probably a lot I've forgotten.
If anyone finds it useful.
Actually my initial inspiration was trekaddicts excellent "Against all Odds" AAR and I would love to try something like that some day but I've never gotten around to playing anyone but the Soviets so this seems increasingly unlikely.
Not sure how good I would be at mastering the naval side of things let alone defending the empire against Germany, Russia and Japan, even with some starting boosts.
