An attack line was a formation of the Imperial Navy commanded by a captain of the line. Attack lines numbered between three to six starships depending on the class of vessels; three ships if the vessels were heavy cruisers or larger, or six if the vessels were light cruisers or frigates. Attack lines supported Star Destroyers or top line capital ships if present, engaging the enemy in range of the Star Destroyer, but outside of the opponent's effective range to damage the Star Destroyer.