Fall back a little and take good care of the only plane you have in the beginning. Send a cavalry to take the depots. The northernmost light artillery will get destroyed by the enemy's medium artillery, as it can't move. Forget it and tighten your line around your HQ. If you want, build a transporter as soon as you can to send it after the cavalry. That way, you get the medium artillery from one of the depots to the frontline faster. By the time the enemy planes arrive, yours should be almost there as well, plus you should have an experienced AA unit.
Once the enemy onslaught is over, take his northern factory, then mop up the rest of his units with planes.
