Here are the two cheats that I know of (there may be more, but the programmers haven't told us about them yet if there are): To be able to play Military vs. Military: At the main screen (with the MISSION BRIEFING, etc. on-screen), press the left and right arrow keys sequentially, i.e., LEFT, RIGHT, LEFT, RIGHT, until the screen flashes. You'll be able to play Mil vs. Mil. To be able to fight the Supervisor: At the main screen, press two lefts then two rights alternately, i.e. LEFT, LEFT, RIGHT, RIGHT, LEFT, LEFT, RIGHT, RIGHT, until the screen flashes. You'll be able to play player vs. player with player 2 as the Supervisor, or you can go to Training and play with the computer as the Supervisor. - Sean TWI Online Support
Written by Sean. Preserved here with the author credited. Original source: The Spoiler.