Surface-to-air missile launcher

In the Halo 3 multiplayer level, High Ground, there appears to be a large three barreled mortar. Bungie staff have called the weapon the Big Ass Mortar Gun.

Nothing is really known about the gun apart from it appears to play a significant part in the Level High Ground (Level) mabye acting like the Automatic Turrets in Snowbound (Level) which shoot players venturing outside map borders. That is very possible, because this picture shows a beach area marked with the text "Mortar Area".