Ship of the line: Meaning (information, definition, explanation, facts)

In the age of sail, after the development of the line of battle in the mid 17th century, and up to the mid 19th century, a ship of the line (of battle) was a warship powerful enough to take a place in the battle line. (The term "battleship" has a similar etymology.) Generally, this meant a third-rate or larger ship, with guns on two or three (or in rare cases, four) decks. Rated ships smaller than this were frigates, which mostly carried all their guns on a single deck. European navies in particular used battleships to fight fleet actions which might last for days and involve over 100 ships.

The rating system of the Royal Navy

From the late 17th to the early 19th centuries, the Royal Navy used the following rating system for its warships:

The number of crew on a first rate was increased by 25 when used as an Admiral's flagship, by 20 with a Vice Admiral and 15 with a Rear Admiral.

Originally from http://www.cronab.demon.co.uk/gen1.htm, with the author's permission.

Isaac Asimov adapted the term "ship of the Line" to apply to the armed spaceships which served a similar role to the old naval vessels for the Galactic Empire of his Foundation trilogy, as mainstays of the space fleet.