My wife had food poisoning (I didn't do it!) so I took care of her yesterday. Now looking at the game state.
The concentration of Allied units in Karelia is dangerous on the defence, but it's very weak on the attack, because the allies cannot all attack in one turn. So your ball of units is largely free to move around unmolested. If you just drove your fifteen tanks in to West Russia, the main attack will be from the British. If they sacrifice everything in Europe, they will reduce you to 7-8 tanks.
If America then commits everything (on their turn), they will likely (65%) finish off the tank stack, and in any case, the survivors will be insufficient to withstand or take Russia.
On the other hand, if you have a bunch of meatsack infantry to protect your tanks, you can pretty much move this ball of death towards Moscow and destroy everything in the way.
On the other-other-hand, if you can remove the Allied presence in Karelia completely without losing your whole frickin' army, you can consider it victory in Europe.
If you contribute all your available ground units (including the tanks in Germany) it is pretty much a 50-50 thing. If you also contribute your aircraft, it becomes a massive landslide in your favor, even with the enemy AA gun present. You're likely to end with those same 6-7 tanks, but no real US/UK presence to worry about for a turn or two. Not a bad situation. Your fighters can also recall to West Europe to cover the zone from other allied attacks.
An all out attack on Karelia is a viable option, however, it should *be* an all out attack, and don't send anything off to Ukraine. Make sure to blitz a tank through Belorussia on the way to Karelia, too.
Other considerations:
Western Europe.
The allies can bring in the UK turn, 1 bomber, 5 infantry and 3 artillery against Western Europe (or 3 artillery/3 infantry against Germany).
With only 2 fighters, you can easily repel this attack - average four infantry + 2 fighters remaining.
Note that if you haven't attacked Karelia, the British can also send some fighters from there, which pitches the odds in their favor as it stands.
The US can bring a bomber, two fighters, 3 infantry, and an artillery.
If the British sacrifice everything, then the US attack *may* succeed. In any case, it's a very favorable trade for us, because the Allies have to sacrifice many expensive units to *possibly* secure the zone, and we can easily retake it with this turn's reinforcements from Germany. Your AA gun is also likely to pluck a fighter or two out of the sky, making it even harder for the enemy to take.
More concerning is Southern Europe, which is completely empty, and now has an enemy transport in range. America will probably want to keep ferrying troops across to Algeria. If they move their naval group in for Southern Europe, this will cost them in the long run.
I would reinforce Southern Europe only lightly; if USA wants to attack Southern Europe, they have to commit quite deeply into the Mediterranean, in range of your aircraft and naval vessels. You can also easily repulse an attack on Southern Europe. The Mediterranean is a dangerous place for your ships and also for USA because both nations have bombers and fighters to significantly alter the balance of power. If you want to go Navy, buy a carrier and put your existing fighters on it, and essentially blow this turns income on more naval units. Point-for-point, a submarine has the same cost-effectiveness as a destroyer, but destroyers can hit air so favor destroyers over submarines where possible.
Lastly, note that USA has 3 fighters and a bomber in range of your current Navy. This is likely enough to take out your ships, with a trade of one-to-two fighters if you're lucky. There's not much you can do to save your Navy if USA wants to take it out this turn. The US air may be more invested in the Japanese army, though, so who knows.
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If you decide not to go all out for Karelia, then dropping everything in to Ukraine is an excellent alternative option, since we are both then threatening Caucacus, the main land bridge between Africa and Europe. Make sure to blitz a tank through Belorussia, and leave one infantry in Belorussia to prevent the Allies from doing the same.
Your units also threaten Eastern Europe should the enemy elect to advance.
I would send your 9 infantry from Germany to the Balkans, and then the Ukraine, because if they go Eastern Europe-to-Ukraine, Karelia will smash them.
Make sure to leave a single infantry in Eastern Europe
so that enemies can't blitz straight through to Germany. A sea invasion of Germany is unfavorable at this time, but if the Brits can drive tanks in as well, it becomes a promising option.
This leaves you in a strong position without risking much. It mainly maintains the current status-quo while slightly improving your situation.
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Purchases - you need to (presently) maintain 3 tanks or two fighters in Germany, plus a bunch of infantry (8 or more) to dissuade allied landings.
You currently have 3 tanks and a maximum production of ten units in the zone.
So I'd keep one or more of these tanks in Germany as your rearguard, and send the rest off to fight in Ukraine.
You have nine infantry in Germany. Decide how many you want to purchase this turn, and send the difference off to Balkans.
You may also buy a fighter to squeeze in an extra production slot.
So maybe something like
1 fighter
1 tank
7 infantry.
Deploy 2 infantry in Southern Europe, and the rest in Germany, you currently have nine, so that means you can send five infantry to the Balkans.
Your new fighter counts as one-and-a-half tanks on defense, and you just built another tank, so you can send all two tanks off to the Ukraine. At a later date, build another fighter, and you don't need tanks in Germany any more.
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Overall....
Completely destroying the Allied presence (as well as both the Russian fighters) in Karelia could be a game winning move. This may also be your only window of opportunity to strike at Karelia before the allies can reinforce further, as they seem want to do. Conversely, the Ukraine approach does improve your situation notably without risking anything.
I think that either approach is viable. But make sure you commit to one, and do not try to do too many things at once.
This is also the turn where you decide if you are going to contest Africa (requires Navy) or not. My feeling is that you have already lost momentum and that this is too difficult to achieve at this point in time - stick to purchasing aircraft, which can tri-purpose as land attack/defense, as well as exert their own coastal influence.