In historical naval usage, a long gun was the standard type of cannon mounted by a sailing vessel, so called to distinguish it from the much shorter carronades. The long gun was known for its increased range and improved mobility in comparison to its larger precursors. This allowed the long gun to establish itself as the best form of artillery to pursue an enemy.
In informal usage, the length was combined with the weight of shot, yielding terms like "long nines", referring to full-length, 9-pounder guns.