How do I defeat the marmota?

The question is pretty much at the title.

How do I defeat the Marmota in chapter 18 of Valkyria Chronicles?
I can't get near it with my tanks, it destroys any unit that approaches it. I was about to give up when I decided to give it one last try.

To take out the lance, I kinda cheated and put heavy armour on the Edelweiss, drove it into the tracks in front of the Marmota so its main gun was at an angle where could hit the lance.

Otherwise, focus on taking out Lancers and Snipers first. And use your Lancers to take out the radiators to drop the shield. You will need an Engineer to restock ammo and don't be afraid to spam CP on one Lancer so you can fire off more shots at the radiators/lance.