In the middle of war, you should not hesitate at shooting the enemies or you will be easily be shot dead. You need to focus on only one thing and that is to kill the enemies. Those enemies will not hesitate on killing you and you should treat them the same. You should be tough and always ready to fight. Aside from that, you should have lots of bullets. If you lack any of these two then you are at a disadvantage here. That is what you need to understand in the middle of war and you enemies know that already.
The truck drives by its own and you will need to defend it from the attackers. Fire at will whenever you see some enemy trailing behind the truck. At the need of each level, you would earn money, which you can use to buy some upgrades for you and the truck. You will also need to repair the truck at some point because it will suffer damage because of the enemies. Hire a gun man to protect it and mount a weapon at the top of the truck to help you defend the truck. The game ends once the truck crash.