The rank in the Royal Navy
indicating the receipt of a commission
as officer in command of a Post Ship
(a Rated ship, one having no less than 20 guns).
This commission entitled a full-grade Captain (officially called a Post-Captain) to a Master, who was responsible for the navigation of the ship, as well as to position in the order of seniority on the list of Captains.
The Post-Captain was distinguished from a Master and Commander, an officer of inferior rank who was given the courtesy title of Captain while serving as an acting Captain, and from a Lieutenant commanding an unrated vessel (a ship of fewer than 20 guns).
Officially, the term Post Captain was used until 1824, at which time it was replaced with Captain. Officers appointed to command post ships and up were technically the only ones to be called Captains, but unofficially the courtesy use of Captain for a Master and Commander or Lieutenant commanding a smaller vessel continued.
--A Sea of Words, A Lexicon and Companion for Patrick O'Brian's Seafaring Tales. Dean King, with John B. Hattendorf and J. Worth Estes. Henry Holt and Company, 1995.
In 1803 Napoleon breaks the Peace of Amiens, and Captain Jack Aubrey, R.N., taking refuge in France from his creditors, is interned. He escapes from France, from debtors' prison, from a possible mutiny, and pursues his quarry straight into the mouth of a French-held harbor.
Post Captain is the second of Patrick O'Brian's 20 tales of the British Royal Navy during the Napoleonic Wars, featuring the exploits of "Lucky Jack" Aubrey and his bosom companion, the mysterious naturalist and spy, Dr. Stephen Maturin.
It's that rare second book--better than the first, and I believe Post Captain is the volume that really puts the O'Brian hooks into a reader. It's impossible NOT to continue with the rest of the series after reading this one. This may explain the phenomenon of the book's disappearing from the shelves of book stores and libraries. I looked for it at Powell's City of Books in Portland one time for a friend and they didn't have it. I was stunned. Powell's didn't have it? They have everything
Post Captain is the one that can be hard to find, though all the books are in print in both hardcover and paperback.
Try to read them in order, as the characters age throughout the series, like the fine wine of which they are so fond.
"Master and Commander raised almost dangerously high expectations; Post Captain triumphantly surpasses them...a brilliant book."--Mary Renault
"The best thing afloat since Horatio Hornblower."--Observer
"Aubrey and Maturin compose one of those complex and fascinating pairs of characters which have inspired thrilling stories of all kinds since the Illiad"--Iris Murdoch and John Bayley