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.