The ships private number and recognition code for the day was of greater importance to establish the bone fides of
another ship than the instruction signal it may have been flying John. If an Admiral sent a signal to the Fleet once action was joined, it was probably too late for the enemy Admiral to react without throwing his ships into chaos even if he had the signal book. Unless it was an encounter battle, most Admirals had already outlined their plans to the captains under them, and as Nelson said, a standing rule of his was that when circumstances changed, any ship who closely engaged the nearest enemy could not be doing wrong. Nevertheless, it seems astounding in today's world that such important information was so easily obtainable.

Rob.