When you try to enter a sector that is occupied by another tank, you are given the option of joining Battle Mode.
In Battle Mode, each side throws waves of units at the other. The attacker goes first, and the battle runs by turns until one side has no units - at which point the surviving player is declared the winner and the loser is destroyed and teleported to their home sector.
By default, you will only deploy a few waves of hippies, but you can customize your battle mode maps by saving special map names. To set up an attack wave, build a map with a single command post anywhere, and whatever MOBILE units you want along the left edge of the map, like the picture to the right.
Then, save the map with the name "attack_wave_1" by running the command
This can be repeated any number of times , in other words the same map saved as
would give you a second attack wave of tanks. Only mobile units will be deployed in battle mode, so putting down silos, mines, etc on battlemode maps is a waste of money.
Your defense waves can be set up the same way, except when you build the maps, put all the units along the RIGHT side of the map instead of the left, and save your units with the command "smap defense_wave_X".
Allies can fight each other in battle mode, so be careful not to anger your friends by attacking them.
Also remember battle mode is very costly because each unit deployed costs money, and they are only active for the battle - so unless you have a far greater economy than your opponent, it should be used only as a last resort when you have to move into sectors that contain other tanks.
You can never attack a tank in its home sector in battle mode, so you can lose at most once when you are offline.