Make an armored car with 15mms of armor and a turret that rotates using electricity mounted with a .60 cal Horsekiller modified to be automatic. The vehicle should only be as big as it has to be to hold the crew and the engine to minimize silhouette. The hull should be friendly to infantry desant. It should have a top speed of at least 20 mph cross-country.
We'd wreck shit on the plains and the mountains with this. Armor's too thick for the vehicle to be damaged by anything less than an artillery shell landing quite close or a direct hit from an 8cm mortar. They'll need anti-tank rifles.
+1. Next turn, we should add armor to our uniform, as I suggested earlier. We're losing too many to shrapnel.
Actually, why are we using a horsekiller, and not trying to jam a stallion in there?
Why not both? .60 explosive rounds (we'd have to invent those first of course) for trashing emplacements and scattering enemy infantry, and a .30 for suppression. But that seems expensive. You're right though. All our infantry already carry .60 rifles as a standard. If we gave the car a .30 then even if the enemy reacted with their own armored vehicles we'd still have the advantage since our guys would be able to take them out.
The Arsetoastkuns have an exploitable advantage right now. They've got no big LOS guns. If we come out with some armor that's immune to their artillery, then we'll definitely gain ground.
E: 15mms of frontal armor would be best. 8mms is about as thick as your finger; it'd protect you from shrapnel, but 7.62 rifle or machine gun rounds would punch right through. It's very little metal compared to the amount you need for howitzers.