Unless you're unlucky enough to be trapped somewhere with just one book, newcomers to Hornblower are faced with a key decision: to read the books in the order Forester wrote them, or in the order of their internal chronology. For instance, 'The Happy Return' introduced the world to Hornblower, but the series has five other books with events predating those of 'The Happy Return'.
There's no right answer here. Read the books in chronological order and you follow Hornblower through his career and across the development of the Napoleonic Wars. In contrast, reading the books in the order of Forester's creation allows for a much easier introduction ('The Happy Return' is deliberately welcoming to new readers) and a chance to miss contradictions, as Forester sometimes changed his mind or made errors and assumptions which are much more obvious in a chronological reading. The decision will differ depending on each reader, but both orders are as follows (titles in brackets are U.S. titles):
Order of Creation
The Happy Return (Beat to Quarters)
A Ship of the Line (Ship of the Line)
Flying Colours
The Commodore (Commodore Hornblower)
Lord Hornblower
Mr Midshipman Hornblower
Lieutenant Hornblower
Hornblower and the Atropos
Hornblower in the West Indies (Admiral Hornblower in the West Indies)
Hornblower and the Hotspur
Hornblower and the Crisis - unfinished (Hornblower in the Crisis)
Chronological order
Mr Midshipman Hornblower
Lieutenant Hornblower
Hornblower and the Hotspur
Hornblower and the Crisis - unfinished* (Hornblower during the Crisis)
Hornblower and the Atropos
The Happy Return (Beat to Quarters)
A Ship of the Line (Ship of the Line)
Flying Colours
The Commodore (Commodore Hornblower)
Lord Hornblower
Hornblower in the West Indies (Admiral Hornblower in the West Indies)
* Many editions of this unfinished novel include two short stories, one set when the hero is a Midshipman and to be read after 'Mr Midshipman Hornblower', while the second is set in 1848 and should be read last.
