Mahan on naval warfare

by A. T. Mahan

1. There is central position, illustrated by France; her national power and control interposing by land between her enemies. Yet not by land only, provided the coast supports an adequate navy; for, if that be the case, the French fleet also interposes between Spanish and Italian ports. The Danube is similarly an instance of central position.

2. Interior lines. The characteristic of interior lines is that of the central position prolonged in one or more directions, thus favoring sustained interposition between separate bodies of an enemy; with the consequent power to concentrate against either, while holding the other in check with a force possibly distinctly inferior. An interior line may be conceived as the extension of a central position, or as a series of central positions connected with one another, as a geometrical line is a continuous series of geometrical points. The expression “Interior Lines” conveys the meaning that from a central position one can assemble more rapidly on either of two opposite fronts than the enemy can, and therefore can utilize force more effectively. Particular examples of maritime interior lines are found in the route by Suez as compared with that by the Cape of Good Hope, and in Panama contrasted with Magellan. The Kiel Canal similarly affords an interior line between the Baltic and North Sea, as against the natural channels passing round Denmark, or between the Danish Islands,—the Sound and the two Belts.[^[22]] These instances of “Interior” will recall one of your boyhood’s geometrical theorems, demonstrating that, from a point interior to a triangle, lines drawn to two angles are shorter than the corresponding sides of the triangle itself. Briefly, interior lines are lines shorter in time than those the enemy can use. France, for instance, in the case before us, could march twenty thousand men to the Rhine, or to the Pyrenees, or could send necessary supplies to either, sooner than Spain could send the same number to the Rhine, or Austria to the Pyrenees, granting even that the sea were open to their ships.

3. The position of France relatively to Germany and Spain illustrates also the question of communications. “Communications” is a general term, designating the lines of movement by which a military body, army or fleet, is kept in living connection with the national power. This being the leading characteristic of communications, they may be considered essentially lines of defensive action; while interior lines are rather offensive in character, enabling the belligerent favored by them to attack in force one part of the hostile line sooner than the enemy can reinforce it, because the assailant is nearer than the friend. As a concrete instance, the disastrous attempt already mentioned, of Spain in 1639 to send reinforcements by the Channel, followed the route from Corunna to the Straits of Dover. It did so because at that particular moment the successes of France had given her control of part of the valley of the Rhine, closing it to the Spaniards from Milan; while the more eastern route through Germany was barred by the Swedes, who in the Thirty Years’ War were allies of France. The Channel therefore at that moment remained the only road open from Spain to the Netherlands, between which it became the line of communications. Granting the attempt had been successful, the line followed is exterior; for, assuming equal rapidity of movement, ten thousand men starting from central France should reach the field sooner.

The central position of France, therefore, gave both defensive and offensive advantage. In consequence of the position she had interior lines, shorter lines, by which to attack, and also her communications to either front lay behind the front, were covered by the army at the front; in other words, had good defense, besides being shorter than those by which the enemy on one front could send help to the other front. Further, by virtue of her position, the French ports on the Atlantic and Channel flanked the Spanish sea communications.

At the present moment, Germany and Austria-Hungary, as members of the Triple Alliance, have the same advantage of central and concentrated position against the Triple Entente, Russia, France, and Great Britain.

Transfer now your attention back to the Danube when the scene of war is in that region; as it was in 1796, and also frequently was during the period of which we are now speaking.... You have seen before, that, if there be war between Austria and France, as there so often was, the one who held the Danube had a central position in the region. Holding means possession by military power, which power can be used to the full against the North or against the South—offensive power—far more easily than the South and North can combine against him; because he is nearer to each than either is to the other. (See map.) Should North wish to send a big reinforcement to South, it cannot march across the part of the Danube held, but must march around it above or below; exactly as, in 1640, reinforcements from Spain to the Rhine had, so to say, to march around France. In such a march, on land, the reinforcement making it is necessarily in a long column, because roads do not allow a great many men to walk abreast. The road followed designates in fact the alignment of the reinforcement from day to day; and because its advance continually turns the side to the enemy, around whom it is moving, the enemy’s position is said to flank the movement, constituting a recognized danger. It makes no difference whether the line of march is straight or curved; it is extension upon it that constitutes the danger, because the line itself, being thin, is everywhere weak, liable to an attack in force upon a relatively small part of its whole. Communications are exposed, and the enemy has the interior line....

This is an illustration of the force of Napoleon’s saying, that “War is a business of positions.” All this discussion turns on position; the ordinary, semi-permanent, positions of Center, North, and South; or the succession of positions occupied by the detachment on that line of communications along which it moves. This illustrates the importance of positions in a single instance, but is by no means exhaustive of that importance. Fully to comprehend, it is necessary to study military and naval history; bearing steadily in mind Napoleon’s saying, and the definitions of central position, interior lines, and communications.

Take, for example, an instance so recent as to have been contemporary with men not yet old,—the Turkish position at Plevna in 1877. This stopped the Russian advance on Constantinople for almost five months. Why? Because, if they had gone on, Plevna would have been close to their line of communications, and in a central position relatively to their forces at the front and those in the rear, or behind the Danube. It was also so near, that, if the enemy advanced far, the garrison of Plevna could reach the only bridge across the Danube, at Sistova, and might destroy it, before help could come; that is, Plevna possessed an interior line towards a point of the utmost importance. Under these circumstances, Plevna alone arrested the whole Russian movement. In the recent war between Japan and Russia,[^[23]] the Port Arthur fleet similarly threatened the Japanese line of communications from Japan to Manchuria, and so affected the whole conduct of the war. It was central, as regards Japan and Liao-Yang, or Mukden. Study of such conditions reinforces knowledge, by affording numerous illustrations of the effect of position under very differing circumstances.

Let us now go back from the Danube with its Center, North, and South, to the communications between the Spanish coast and the Austrian army in Germany. Should the House of Austria in Spain desire to send large reinforcements to the Danube, or to the Rhine, by way of Italy, it can do so, provided it controls the sea; and provided also that France has not shaken its hold upon North Italy. Such a condition constitutes open and safe communications. If, however, command of the sea is not assured, if the French navy, say at Toulon, is equal to the Spanish navy in the neighborhood, there is danger of a reverse; while if the French navy is superior locally, there is great danger not merely of a reverse but of a serious disaster. In such a case the French navy, or the port of Toulon, flanks the Spanish line of communication; again an instance of position. As to position, Toulon would correspond to Plevna and Port Arthur. This instance illustrates, however, as Port Arthur conspicuously did, that the value of a position is not in the bare position, but in the use you make of it. This, it is pertinent to note, is just the value of anything a man possesses, his brains or his fortune—the use he makes of either. Should the French navy be decisively inferior locally to the Spanish, Toulon loses its importance. As position it is still good, but it cannot be used. It is an unavailable asset. So at Plevna, had the garrison been so small that it could not take the field, the place either would have been captured, or could have been watched by a detachment, while the main Russian body moved on. At Port Arthur, the inefficiency of the Russian navy permitted this course to the Japanese. They watched the place by navy and army, and went on with their march in Manchuria. Even so, the threat inherent in the position compelled an immense detachment of troops necessary for the siege, and so greatly weakened the main army in its action.