The Canopus-class ships of the line were a class of nine 84-gun two-deck second rates of the Royal Navy. Their design was based on an enlarged version of the lines of the captured French ship Franklin, since commissioned in the Royal Navy as HMS Canopus, although this ship herself was not included as a member of the class. The earlier ships were initially ordered as 80-gun third rates, but this classification was altered by changes in the rating system in February 1817. This class of ships is sometimes referred to as the Formidable class.