Secondly, there is the relation of the speed of convoys to the speed of cruisers and flotilla; that is to say, our ability to get contact with a convoy after it has put to sea and before the expedition can be disembarked is as the speed of our cruisers and flotilla to the speed of the convoy.
Thirdly, there is the relation between the destructive power of modern cruisers and flotillas against a convoy unescorted or weakly escorted and the corresponding power in sailing days.
Fourthly, there is the relation between the speed of convoys and the speed of battle-squadrons, which is of importance where the enemy's transports are likely to be strongly escorted. On this relation depends the facility with which the battle-squadron covering our mobile defence can secure an interior position from which it may strike either the enemy's battle-squadron if it moves or his convoy before it can complete its passage and effect the landing.
All these relations appear to have been modified by modern developments in favour of the defence. In the first ratio, that of speed of mobilisation to speed of intelligence, it is obviously so. Although military mobilisation may be still relatively as rapid as the mobilisation of fleets, yet intelligence has outstripped both. This is true both for gaining and for conveying intelligence. Preparations for oversea invasion were never easy to conceal, owing to the disturbance of the flow of shipping that they caused. Elaborate precautions were taken to prevent commercial leakage of intelligence, but they never entirely succeeded. Yet formerly, in the condition of comparative crudeness with which international trade was then organised, concealment was relatively easy, at least for a time. But the ever-growing sensitiveness of world-wide commerce, when market movements are reported from hour to
hour instead of from week to week, has greatly increased the difficulty. And apart from the rapidity with which information may be gathered through this alert and intimate sympathy between Exchanges, there is the still more important fact that with wireless the speed of conveying naval intelligence has increased in a far higher ratio than the speed of sea transit.
As regards the ratio between cruiser and convoy speeds, on which evasion so much depends, it is the same. In frigate days the ratio appears to have been not more than seven to five. Now in the case at any rate of large convoys it would be nearly double.
Of the destructive power of the flotilla, growing as it does from year to year, enough has been said already. With the advent of the torpedo and submarine it has probably increased tenfold. In a lesser degree the same is true of cruisers. In former days the physical power of a cruiser to injure a dispersing convoy was comparatively low, owing to her relatively low excess of speed and the restricted range and destructive power of her guns. With higher speed and higher energy and range in gun power the ability of cruisers to cut up a convoy renders its practical annihilation almost certain if once it be caught, and consequently affords a moral deterrent against trusting to evasion beyond anything that was known before.
The increased ratio of battle-fleet speed to that of large convoys is equally indisputable and no less important, for the facility of finding interior positions which it implies goes to the root of the old system. So long as our battle-fleet is in a position whence it can cover our flotilla blockade or strike the enemy's convoy in transit, it forces his battle-fleet in the last resort to close up on the convoy, and that, as Kempenfelt pointed out, is practically fatal to the success of invasion.
From whatever point of view, then, we regard the future chances of successful invasion over an uncommanded sea, it
would seem that not only does the old system hold good, but that all modern developments which touch the question bid fair to intensify the results which our sea service at least used so confidently to expect, and which it never failed to secure.