Such were the signal books in use at Trafalgar, and in the hands of a man like Nelson, who did not keep his tactical ideas to himself, but discussed them freely with his captains during the months of watching and preparation, they proved amply sufficient for the purpose.
But suppose the books were captured by the enemy; how then? In such an event, which all captains were told to guard against by throwing the books overboard if there was any probability of their ship being captured, the most effective precaution was to change the whole of the signal numbers, both in the general signals and in the vocabulary, but this was a heavy task.
A less effective method was to transpose all the flags. It was less effective since, ex hypothesi, the enemy had the signal books, they had therefore only to note the colours of the flags which preceded some easily recognised manoeuvre, such as "Make more sail," "Bear up and sail large," to discover what flags were now being used to indicate the signal numbers which they saw against that signal. A little patience and ingenuity would then supply the key to the changes in the flags, whereas if all the signal numbers were irregularly transposed, each signal would have to be re-constituted separately by the enemy.
About fifteen months before Trafalgar the 12-gun schooner, 'Redbridge,' commanded by a Lieut. Lemprière, who, to judge by Nelson's remarks about him, was not particularly efficient, was captured by some French frigates off Toulon. Such a small ship, commanded by an officer of such subordinate rank, was not allowed the confidential signal books, but Lemprière had, in common with many other junior officers, obtained a surreptitious copy for himself—one of those little manuscript and hand-painted signal books one sees in museums, or occasionally picks up in second-hand book shops.
This book Lieut. Lemprière had neglected to throw overboard, and when, later on, one of Nelson's scouts, looking into Toulon harbour to see if the French were getting on comfortably, found the captured 'Redbridge' just outside, the latter made the signal for the scout ship to anchor; but fortunately the officer in command was a little sharper than the 'Redbridge's' late commander had been, and the net was spread in vain.
Directly Nelson learned this he changed the flags and reported the matter to the Admiralty. On the 4th November, the Admiralty, despite the objection of Lord Keith that a change of signal numbers would be better, issued a circular letter to all commanders-in-chief telling them to alter their numeral flags in accordance with a painted copy enclosed with the letter. These are the flags shown in the third column of the plate. Further, as their Lordships had reason to apprehend that Lieut. Lemprière was not the only officer under commander's rank who had obtained a copy of the signal book, the strictest injunctions were to be given that such improper proceedings were not to take place in future, and existing irregular copies were to be impounded.
The flags in use in the Mediterranean were changed in numerical value in accordance with the Admiralty order on the 16th January, 1804, and these new numeral flags were the ones used at Trafalgar, and, in fact, until the end of 1810[390].
We have seen that Howe's second code, first in its original form, next as re-arranged by McArthur, and finally as simplified and expanded for the 1799 Signal Book, in each case with practically the same numeral flags, sufficed, when supplemented by Popham's Vocabulary, for the navy's needs throughout the most sustained and strenuous struggle that until the recent war had ever fallen to its lot[391].
Towards the close of this period, however, Popham, who seems to have devoted all the time not required for his professional duties, or for defence against the attacks made upon him, to the improvement of his code[392], brought out a greatly enlarged and improved vocabulary, which is best described in his own words:
The present edition is wholly new cast and composed; very considerably enlarged by additional materials; and, as I trust, improved by a distribution of those materials which was intended to increase the facility of reference.