Surface-to-Air Missile Launcher

In the Halo 3 multiplayer level, High Ground, there appears to be what Bungie staff have called the Big Ass Mortar Gun (See Image).

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.