In the British Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

, a third rate was a ship of the line

Ship of the line

A ship of the line was a type of naval warship constructed from the 17th through the mid-19th century to take part in the naval tactic known as the line of battle, in which two columns of opposing warships would manoeuvre to bring the greatest weight of broadside guns to bear...

 which from the 1720s mounted between 64 and 80 guns, typically built with two gun deck

Gun deck

The term gun deck originally referred to a deck aboard a ship that was primarily used for the mounting of cannon to be fired in broadsides. However, on many smaller vessels such as frigates and unrated vessels the upper deck, forecastle and quarterdeck bore all of the cannons but were not referred...

s (thus the related term two-decker

Two-decker

A two-decker is a sail warship which carried her guns on two fully armed decks. Usually additional guns were carried on the upper works , but this was not a continuous battery, so were not counted....

). Years of experience proved that the third rate ships embodied the best compromise

Optimization (mathematics)

In mathematics, computational science, or management science, mathematical optimization refers to the selection of a best element from some set of available alternatives....

 between sailing ability (speed, handling), firepower, and cost. So, while first rates and second rates were both larger and more powerful, the third-rate ships were in a real sense the optimal configuration.

Rating

When the rating system was first established in the 1620s, the third rate was defined as those ships having at least 200 but not more than 300 men. By the 1660s, the means of classification had shifted from the number of men to the number of carriage-mounted guns, and third rates at that time mounted between 48 and 60 guns. By the turn of the century, the criteria had grown and third rate carried more than 60 guns, with second rates having between 90 and 98 guns, while first rates had 100 guns or more, and fourth rates between 48 and 60 guns. By the latter half of the 18th century, they carried between 500 and 720 men.

This designation became especially common because it included the 74-gun ship, which eventually came to be the most popular size of large ship for navies of several different nations. It was an easier ship to handle than a first- or second-rate ship, but still possessed enough firepower to potentially destroy any single opponent other than a three-decker. It was also cheaper to operate.

Although this rating system was only used by the Royal Navy, British authors might still use "third rate" to speak of a French 74 (although the French Navy had its own system of five rates or rangs). By the end of the 18th century, ships of the line were usually characterized directly by their number of guns, the numbers even being used as the name of the type, as in "a squadron of three 74s". However, the rating system, although modified in 1817, continued until the end of the Age of Sail

Age of Sail

The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...

.