The tournament organizers at Liandri have decided that the recreation of arguably the Earth’s most violent war would create the perfect arena of combat. Storming the beaches of Normandy in WWII was chosen in particular because of the overwhelming odds facing each member of the attacking force. Defending this beach, however, will prove to be no less of a daunting task.
In order to disable the Long-Range-Cannon you must make your way through the defenders’ base to the large Gun Cavern deep inside the cliff wall. In there, you will find the ‘Main Gun Control’ room. Destroy the equipment in that room.