POSTSCRIPT
The question of 'Communications,' if fully dealt with in the foregoing paper, would have made it so long that its hearers might have been tired out before its end was reached. The following summary of the points that might have been enlarged upon, had time allowed, may interest many officers:—
In time of war we must keep open our lines of communication.
If we cannot, the war will have gone against us.
Open communications mean that we can prevent the enemy from carrying out decisive and sustained operations against them and along their line.
To keep communications open it is not necessary to secure every friendly ship traversing the line against attacks by the enemy. All that is necessary is to restrict the enemy's activity so far that he can inflict only such a moderate percentage of loss on the friendly vessels that, as a whole, they will not cease to run.
Keeping communications open will not secure a friendly place against every form of attack. It will, however, secure a place against attacks with large forces sustained for a considerable length of time. If he can make attacks of this latter kind, it is clear that the enemy controls the communications and that we have failed to keep them open.
If communications are open for the passage of vessels of the friendly mercantile marine, it follows that the relatively much smaller number of supply-vessels can traverse the line.
As regards supply-vessels, a percentage of loss caused by the enemy must be allowed for. If we put this at 10 per cent.—which, taken absolutely, is probably sufficient—it means that _on_the_ average out of ten supply-vessels sent we expect nine to reach their destination.
We cannot, however, arrange that an equal loss will fall on every group of ten vessels. Two such groups may arrive intact, whilst a third may lose three vessels. Yet the 10 per cent. average would be maintained.