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.