War is the method adopted, when less violent means of persuasion have failed, to force your enemy to comply with your demands. There are three principal ways of effecting this—invasion of his country, raids on his territory, destruction or serious damage of his sea-borne commerce. Successful invasion must compel the invaded to come to terms, or his national existence will be lost. Raids upon his territory may possibly so distress him that he would rather concede your terms than continue the struggle.[90] Damage to his sea-borne commerce may be carried so far that he will be ruined if he does not give in. So much for one side of the account; we have to examine the other. Against invasion, raids, or attempts at commerce-destruction there must be some form of defence, and, as a matter of historical fact, defence against each has been repeatedly successful. If we need instances we have only to peruse the history of the British Empire.
[Footnote 90: Though raids rarely, if ever, decide a war, they may cause inconvenience or local distress, and an enemy desiring to make them should be obstructed as much as possible.]
How was it that—whilst we landed invading armies in many hostile countries, seized many portions of hostile territory, and drove more than one enemy's commerce from the sea—our own country has been free from successful invasion for more than eight centuries, few portions of our territory have been taken from us even temporarily, and our commerce has increased throughout protracted maritime wars? To this there can only be one answer, viz. that the arrangements for defence were effectual. What, then, were these arrangements? They were comprised in the provision of a powerful, well-distributed, well-handled navy, and of a mobile army of suitable strength. It is to be observed that each element possessed the characteristic of mobility. We have to deal here more especially with the naval element, and we must study the manner in which it operates.
Naval war is sea-power in action; and sea-power, taken in the narrow sense, has limitations. It may not, even when so taken, cease to act at the enemy's coast-line, but its direct influence extends only to the inner side of a narrow zone conforming to that line. In a maritime contest each side tries to control the ocean communications and to prevent the other from controlling them. If either gains the control, something in addition to sea-power strictly defined may begin to operate: the other side's territory may be invaded or harassed by considerable raids, and its commerce may be driven from the sea. It will be noticed that control of ocean communications is the needful preliminary to these. It is merely a variant of the often employed expression of the necessity, in war, of obtaining command of the sea. In the case of the most important portion of the British Empire, viz. the United Kingdom, our loss of control of the ocean communications would have a result which scarcely any foreign country would experience. Other countries are dependent on importations for some part of the food of their population and of the raw material of their industry; but much of the importation is, and perhaps all of it may be, effected by land. Here, we depend upon imports from abroad for a very large part of the food of our people, and of the raw material essential to the manufacture of the commodities by the exchange of which we obtain necessary supplies; and the whole of these imports come, and must come to us, by sea. Also, if we had not freedom of exportation, our wealth and the means of supporting a war would disappear. Probably all the greater colonies and India could feed their inhabitants for a moderately long time without sea-borne imports, but unless the sea were open to them their prosperity would decline.
This teaches us the necessity to the British Empire of controlling our maritime communications, and equally teaches those who may one day be our enemies the advisability of preventing us from doing so. The lesson in either case is driven farther home by other considerations connected with communications. In war a belligerent has two tasks before him. He has to defend himself and hurt his enemy. The more he hurts his enemy, the less is he likely to be hurt himself. This defines the great principle of offensive defence. To act in accordance with this principle, a belligerent should try, as the saying goes, to carry the war into the enemy's country. He should try to make his opponents fight where he wants them to fight, which will probably be as far as possible from his own territory and as near as possible to theirs. Unless he can do this, invasion and even serious raids by him will be out of the question. More than that, his inability to do it will virtually indicate that on its part the other side can fix the scene of active hostilities unpleasantly close to the points from which he desires to keep its forces away.
A line of ocean communications may be vulnerable throughout its length; but it does not follow that an assailant can operate against it with equal facility at every point, nor does it follow that it is at every point equally worth assailing. Lines running past hostile naval ports are especially open to assault in the part near the ports; and lines formed by the confluence of two or more other lines—like, for example, those which enter the English Channel—will generally include a greater abundance of valuable traffic than others. Consequently there are some parts at which an enemy may be expected to be more active than elsewhere, and it is from those very parts that it is most desirable to exclude him. They are, as a rule, relatively near to the territory of the state whose navy has to keep the lines open, that is to say, prevent their being persistently beset by an enemy. The necessary convergence of lines towards that state's ports shows that some portion of them would have to be traversed, or their traversing be attempted, by expeditions meant to carry out either invasion or raids. If, therefore, the enemy can be excluded as above mentioned, invasions, raids, and the more serious molestation of sea-borne commerce by him will be prevented.
If we consider particular cases we shall find proof upon proof of the validity of the rule. Three great lines—one from the neighbourhood of the Cape of Good Hope, one from the Red Sea, and a third from India and Ceylon—converge near the south-western part of Australia and run as one line towards the territory of the important states farther east. If an assailant can be excluded from the latter or combined line he must either divide his force or operate on only one of the confluents, leaving the rest free. The farther he can be pushed back from the point of confluence the more effectually will he be limited to a single line, because the combining lines, traced backwards, trend more and more apart, and it is, therefore, more and more difficult for him to keep detachments of his force within supporting distance of each other if they continue to act against two or more lines. The particular case of the approaches to the territory of the United Kingdom has the same features, and proves the rule with equal clearness. This latter case is so often adduced without mention of others, that there is some risk of its being believed to be a solitary one. It stands, however, exactly on all fours with all the rest as regards the principle of the rule.
A necessary consequence of an enemy's exclusion from the combined line as it approaches the territory to be defended is—as already suggested—that invasion of that territory and serious raids upon it will be rendered impracticable. Indeed, if the exclusion be absolutely complete and permanent, raids of every kind and depredations on commerce in the neighbourhood will be prevented altogether. It should be explained that though lines and communications are spoken of, it is the area crossed by them which is strategically important. A naval force, either guarding or intending to assail a line, does not necessarily station itself permanently upon it. All that it has to do is to remain, for the proper length of time, within the strategic area across which the defended or threatened line runs. The strategic area will be of varying extent, its boundaries being determined by circumstances. The object of the defence will be to make the area from which the enemy's ships are excluded as extensive as possible. When the enemy has been pushed back into his own waters and into his own ports the exclusion is strategically complete. The sea is denied to his invading and important raiding expeditions, and indeed to most of his individual cruisers. At the same time it is free to the other belligerent. To effect this a vigorous offensive will be necessary.
The immediate theatre of operations, the critical strategic area, need not be, and often ought not to be, near the territory defended by our navy. It is necessary to dwell upon this, because no principle of naval warfare has been more frequently or more seriously misapprehended. Misapprehension of it has led to mischievous and dangerous distribution of naval force and to the squandering of immense sums of money on local defence vessels; that is, vessels only capable of operating in the very waters from which every effort should be made to exclude the enemy. Failure to exclude him from them can only be regarded as, at the very least, yielding to him an important point in the great game of war. If we succeed in keeping him away, the local defence craft of every class are useless, and the money spent on them has been worse than wasted, because, if it had not been so spent, it might have been devoted to strengthening the kind of force which must be used to keep the enemy where he ought to be kept, viz. at a distance from our own waters.
The demand that ships be so stationed that they will generally, and except when actually cruising, be within sight of the inhabitants, is common enough in the mother country, and perhaps even more common in the over-sea parts of the British Empire. Nothing justifies it but the honest ignorance of those who make it; nothing explains compliance with it but the deplorable weakness of authorities who yield to it. It was not by hanging about the coast of England, when there was no enemy near it, with his fleet, that Hawke or Nelson saved the country from invasion, nor was it by remaining where they could be seen by the fellow-countrymen of their crews that the French and English fleets shut up their enemy in the Baltic and Black Sea, and thus gained and kept undisputed command of the sea which enabled them, without interruption, to invade their enemy's territory.