It is an option you need to unlock.
check out here
http://megusta.tistory.com/31
It will unlock while you play easy levels.
People are not comfortable with this so I'm considering earlier unlock timing.
I LOVE arcade mode, upgrading as I go through, the only downfall...there's no INSERT COIN TO CONTINUE! I hate having to start all over after a boss shits on me. T_T
Missiles from the helicopters need to be able to be shot down (just like the ones from the submarine). So irritating. Other than that....UPGRADES GRIND FEST. WOOOOOOOOO
It is an option you need to unlock. check out here http://megusta.tistory.com/31 It will unlock while you play easy levels. People are not comfortable with this so I'm considering earlier unlock timing.