A Ship of the Line is a naval warship having 50 or more guns for combat. They were designed to form a line of battle. Some had up to 140 guns, but, being three-deckers tend to be unwieldy. The 74 gun ship was the most common, which was a good balance of fire-power and manoeuvrability. Ships of the line were categorized as first through sixth rate.
- Ship of the Line at Wikipedia.