To get Garma's Zaku II, you must destroy a certain number of Dopps in stage two, "Winds of War". When destroying Dopps, you will hear Amuro counting how many Dopps he has destroyed. When he gets to six, he will ask "Who's gonna be seven?" After the seventh Dopp is done, you are able to fight Garma in his Zaku II. You must destroy it before you fight Char. This is difficult, but if you get your timing correct you will be able to defeat him. Also, this must be done in Story mode, not Stage Select. Once your game has been auto-saved after stage two, return to the title screen. It is best to complete the game first to unlock Tactics mode. You must be at least a Major or higher in the Tactics Battle Mode Zeon.