which one is it ?
and where do you get it?
you get it on the outskirts level and when you go into the bridge part(the subway type thing) when it says Loading... turn around and go all the way back to the pelican that was shot down when you first get your first warthog and then just keep going to behind thatand it will be on a balcony. It is awesome!!! You can throw fifty grenades on it and it won't die!!!!