Slitherine

Is it just me, or is this unwinnable on Field Marshall? I managed a triumph at turn 29, but only after cheating for the first time in many years of Panzer Corps, as the 7000ish I had carried over wasn't even enough to get my force - started in 42, FM all the way - into a fully modern fighting shape. That was with careful rationing through the three DLCs, finding plenty of heroes and scavenge, upgrading along responsible lines. I had to grant myself a ton of Prestige to upgrade all armor to M26s that could go toe-to-toe with the endless IS2 and IS3 combos, buy tons of extra 90MM AAA for the endless waves of superior aircraft - it was nuts. I tried 7 times without cheating, I didn't get past the first minor river without being slaughtered in the repeated waves of commies.

Maybe this is a Kobayashi Maru type thing?

I finally managed a triumph on this one, playing on General, and starting with 7000-ish in prestige as well. The first couple of times I played this scenario, I either suffered the devastation that you described, or (to avoid that devastation) I stayed on the defensive for so long that I could not reach the Soviet HQ by Turn 30. I realized that I did not have a sufficiently deep bench, for one thing, so I replayed the entire campaign in order to build up a larger reserve of experienced fighters, tanks, and tank destroyers. That helped enormously this time: as units were destroyed, I was able to feed replacements into the fight without expending prestige.

Here's the strategy that ultimately worked for me: I divided my force into two equal battle groups. My left flank (my left, to the right on the map) advanced quickly, with the ultimate goal of seizing the Soviet HQ. The right flank stayed on the defensive, behind the first river, until the Soviet assault petered out (around Turn 20), and then it advanced rapidly to seize the objectives on the left side of the map. In order to make this work, the two groups have to work independently--if you swing the left flank over to cut off and destroy the main Soviet force, you will leave yourself with too little time to reach the Soviet HQ.