It was upon the tactical system contained in this book that all the great actions of the Nelson period were fought.  The alterations which took place during the war were slight.  The codes used by Howe himself in 1794, and by Duncan at Camperdown in 1797, follow it exactly.  A slightly modified form was issued by Jervis to the Mediterranean fleet, and was used by him at St. Vincent in 1797.  No copy of this is known to exist, but from the logs of the ships there engaged it would appear that, though the numbering of the code had been changed, the principal battle signals remained the same.  In 1799 a new edition was printed in the small quarto form.  In this the Signal Book and the Instructions were bound together, and were issued to the whole navy, but here again, though the numbers were changed, the alterations were of no great importance.[2] Reprints appeared in 1806 and 1808, but the code itself continued in use till 1816.  In that year an entirely new Signal Book based on Sir Home Popham’s code was issued with a fresh set of Explanatory Instructions, or, as they had come to be called, ’Instructions relating to the line of battle and the conduct of the fleet preparatory to their engaging and when engaged with an enemy.’[3] Both these sets of ‘Explanatory Instructions’ are printed below, but, as we have seen, they throw but little light by themselves on the progress of tactical thought during the great period they covered.  They were no longer ‘Fighting Instructions’ in the old sense, unless read with the principal battle signals, and to these we have to go to get at the ideas that underlay the tactics of Nelson and his contemporaries.

Now the most remarkable feature of Howe’s Second Signal Book, 1790, is the apparent disappearance from it of the signal for breaking the line which in his first code, 1782, he had borrowed from Hood in consequence of Rodney’s manoeuvre.  The other two signals introduced by Hood and Pigot for breaking the line on Rodney’s plan are equally absent.  In their stead appears a signal for an entirely new manoeuvre, never before practised or even suggested, so far as is known, by anyone.  The ‘signification’ runs as follows:  ’If, when having the weather-gage of the enemy, the admiral means to pass between the ships of their line for engaging them to leeward or, being to leeward, to pass between them for obtaining the weather-gage.  N.B.—­The different captains and commanders not being able to effect the specified intention in either case are at liberty to act as circumstances require.’  In the Signal Book of 1799 the wording is changed.  It there runs ’To break through the enemy’s line in all parts where practicable, and engage on the other side,’ and in the admiralty copy delivered to Rear-Admiral Frederick there is added this MS. note, ’If a blue pennant is hoisted at the fore topmast-head, to break through the van; if at the main topmast-head, to break through the centre; if at the mizen topmast-head, to break through the rear.’[4]