In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Cannon
If you hear cannon fire then you will receive help from a friend. If you are firing cannonballs then you will enjoy professional success. If, however, you dream that cannons are firing at you then you will experience some problems.