Tankettes rule!
They take only 5 IC, six manpower, are quick to produce, consume zero or minimal supplies and little fuel; and, later on with add-ons get respectable hard, soft and defense values. Plus they're the fastest land unit.
Playing Germany by the time the Allies declare war, I have @90 tankette divisions, with 12 soft attack value. I also have @90 dive bombers, because with CORE they're cheap and fast to produce too.
When war is declared by the allies, (I like to wait for it while I assemble my irresistable force) Poland is reduced in 10 days to a puppet by ferocious assaut.
Then, since all German provinces have been upgraded to 99 infrastructure the tankettes sprint west. They and the bombers are assaulting France in a week, and it falls in two weeks (goes to show you can fight with one hand your back and still kick CORE ass - by wasting IC on infrastructure).
The dive bombers then pound the coast of Britain for a week. Two transports unload two tankette divisions at a time (that's all it takes folks and the trip is short). England should fall in three weeks (it takes a while to get north and there are a lot of English fighter planes).
Then, upgrade all your early tankettes. Position most of the tankettes and dive bombers in Poland one province away from the border. Load Poland up with techs and wait for the Soviet attack.
When they do attack, hit them north and south of the marshes in two big blows of 50+ divisions of tankettes. With the southern attack, drive south to Sebastopol while covering your flank and bag 20 divisions, then move north to surround the south of the marshes.
The northern attack should flank-cover the north and east side of the marshes and also sprint for Moscow. Halt before the capital and wait for a counter-attack: shred it with dive bombers and dug-in tankettes. Then, walk into the city.
Meanwhile, you've totally surrounded the 70+ divisions trapped in the marshes and kept some bombers nearby in case they break out.
There is only one massive Soviet force left, in the north between Moscow and Leningrad. It's too big to dive bomb, but you can pincer it through the forests to it's north and leave it to wither away.
That's all it takes to win in CORE: tankettes, dive bombers, some infantry for occupation and some subs for shredding surface ships.
Ho-hum.