England expects...

[PMarione]

The Nelson's signal at Trafalgar is certainly the most famous signal of British history.
The signal is still hoisted in many places on 21st October anniversary and if I remember well, permanently in the Victory's rigging.

Everybody agrees that the code used was Popham's Marine Vocabulary, and most that the version used was the 1803 edition even if 1805 one was possible.

So the code certainly was 253, 269, 863, 261, 471, 958, 220, 370, 4, 21, 19, 24, the last 4 numbers being alphabetic for DUTY.

The problem is which flags did Pasco use?
Most probably NOT the flags that are generally shown which are the numeral flags, more exactly in the order generally shown.

In 1805, the Popham's code book had been compromized: the Admiralty had good reason to think that a code book had been captured by the French on board a ship, and thence that they could read all the signals.
Write, print and distribute a new code book was very expensive so they opted for a cheap and easy solution: superencipherment meaning encipher the codes. Coding is replacing a word or sentence by a number: 253 = England... Ciphering is replace a symbol by another: A = D, B = E...

So it was simple to assign a different numeral value to the flags: the flag for 1 becoming the flag for 3, 2 = 7...
So it was simple for a CinC to distribute new assignment for numerical flags. He could even give 2 sets to each captain, one for signals to the fleet, one for private messages.

Back to the point: it's most probably certain that Nelson used such superencipherment at Trafalgar.
No picture was taken and no assignment table has survived to my knowledge and so we will never be able to know which exact flags where used for his famous signal except that (most probably) NOT those taken from the code book and displayed today.

Further reading: Harvey G. Cragon, Royal Navy Codes and Ciphers in the Napoleonic Wars, Dallas, 2005, ISBN: 0-9743045-2-2

David Kahn, The Code-breakers, Scribner, 1996, ISBN: 978-0684831305
makes fascinating reading if you are interested in codes and ciphers from Caesar to Enigma and if you want to know how your credit card number is encrypted when you order a good book on this website.

[alexlitandem]

Has this not been resolved?

[ionia]

Patrick - I can't see what this is all about. The story is well known -the schooner REDBRIDGE was captured on 4th August, 1803 and it became known that the French had obtained a manuscript copy of the 1799 signal book which was therefore compromised (Popham's code used the numeral flags of the 1799 book). The Admiralty re-arranged the flags by circular in November, 1803 and the new arrangement was adopted in the Mediterranean Fleet on 16th January 1804.

As far as I am aware, the only doubt about the format of the Trafalgar signal is in relation to whether the No. 4 flag (red and white quarterly) should be hoisted with the red or the white canton upermost to the mast!
_________________
Ionia

[PMarione]

The problem is not with the code book. Most authors agree that the 1803 code book was used as the 1805 version was probably not yet available.

Cragon shows a letter to Heywood (of Bounty fame):

[ionia]

The letter from Young to Heywood (presumably in 1813-14) was designed to facilitate secret messages and to outline communications about mutinous behaviour. (I presume that the signature is that of William Young, Admiral of the White Squadron. He had been a member of the committee of the Board of Admiralty which had made feeble and unsuccessful overtures to the Spithead mutineers in 1797 so the subject of mutiny was probably close to his heart.)

Why should Nelson wish to make a secret of his "England expects..." signal?
_________________
Ionia

[PMarione]

You are probably right but if at the time he was using a superencyphering mode it was used for all signals otherwise how would other ships know what sequence to use?