After you purchase all items in the battle maps mode (like for example missile plains, banker hills Flak etc.. ) but be sure youve beaten the game and have 5000 or more PTS.
(it cost 5000PTS.)
I havent tried it bec. i only see it in the internet (www.gamenowmag.com)
well see you next time (if you can see me!! JOKE!!!!) :)