Pause the game. Press and gold buttons A and B on Controller 1 and button C on Controller 2 at the same time; you'll hear a bubbling sound. Now, while paused, you can access the following features:

Maximim Medics:
Press and hold A and C on Controller 1 and B and Down on Controller2.

Battle Advance:
Press and hold A, C, and Up on Controller 1 and B on Controller 2.

Full-Scale War Advance:
Press and hold A, C, and Up on Controller 1 and B on Controller 2.

These cheats give the victories and/or Medics to the Chaos Army. To give Havoc the benefits, simply reverse the commands: e.g. for max medics, press A + C on Controller 2 and B + Down on Controller 1.