Under No Flag Tank Wave

How am I supposed to take out the 3 tanks that come down the center road at the end of Under No Flag? The nearby Mortar (or some heavy cannon) takes at least 3 shots to take out just one tank and its position get annilated by tank fire before I can even kill one tank, let alone 3. And I haven't found an RPG or similar weapon that could hurt them while staying more mobile. I'm only playing on Medium difficulty and I haven't had an issues during any other part of this initial campaign. And now all of a sudden I'm dying non-stop... but its even worse that I don't even understand how I'm supposed to not die.

Its driving me nuts!