Play as Char Aznable
Get an "S" rank in Simulation Program 1 to unlock Char Aznable.
Play as Garma Zabi
Get an "S" rank in Simulation Program 2 to unlock Garma Zabi.
Play as Sayla
Get three "C" ranks or below on the Federation missions to unlock Sayla.
Additional missions
Successfully complete the game to unlock another set of missions.
Federation Shield for Austin's Zaku 1
Successfully complete the game, then play practice mission 1 with Austin's Zaku 1. Successfully complete it and you should have a heavy Fed shield like the Gundam's, and a few new supplies.