convoy upgrades

I propose that you should be able to upgrade the land ad sea convoys, as this happened regularly in the war. at level one, the convoys are as they are now, but speed and hit point increase regularly until level 3 on. Example, the starting convoy truck moves at 20 km/h, and that speed stays consistent. But near the end of the war, the trucks could reach speeds of 58 km/h. also, different terrains interfered with the trucks speed.