THE roads which lead from the position of an army to those points in its rear where its depôts of supply and means of recruiting and refitting its forces are principally united, and which it also in all ordinary cases chooses for its retreat, have a double signification; in the first place, they are its lines of communication for the constant nourishment of the combatant force, and next they are roads of retreat.
We have said in the preceding chapter, that, although according to the present system of subsistence, an army is chiefly fed from the district in which it is operating, it must still be looked upon as forming a whole with its base. The lines of communication belong to this whole; they form the connection between the army and its base, and are to be considered as so many great vital arteries. Supplies of every kind, convoys of munitions, detachments moving backwards and forwards, posts, orderlies, hospitals, depôts, reserves of stores, agents of administration, all these objects are constantly making use of these roads, and the total value of these services is of the utmost importance to the army.
These great channels of life must therefore neither be permanently severed, nor must they be of too great length, or beset with difficulties, because there is always a loss of strength on a long road, which tends to weaken the condition of an army.
By their second purpose, that is as lines of retreat, they constitute in a real sense the strategic rear of the army.
For both purposes the value of these roads depends on their length, their number, their situation, that is their general direction, and their direction specially as regards the army, their nature as roads, difficulties of ground, the political relations and feeling of local population, and lastly, on the protection they derive from fortresses or natural obstacles in the country.
But all the roads which lead from the point occupied by an army to its sources of existence and power, are not on that account necessarily lines of communication for that army. They may no doubt be used for that purpose, and may be considered as supplementary of the system of communication, but that system is confined to the lines regularly prepared for the purpose. Only those roads on which magazines, hospitals, stations, posts for despatches and letters are organised under commandants with police and garrisons, can be looked upon as real lines of communication. But here a very important difference between our own and the enemy's army makes its appearance, one which is often overlooked. An army, even in its own country, has its prepared lines of communication, but it is not completely limited to them, and can in case of need change its line, taking some other which presents itself, for it is every where at home, has officials in authority, and the friendly feeling of the people. Therefore, although other roads may not be as good as those at first selected there is nothing to prevent their being used, and the use of them is not to be regarded as impossible in case the army is turned and obliged to change its front. An army in an enemy's country on the contrary can as a rule only look upon those roads as lines of communication upon which it has advanced; and hence arises through small and almost invisible causes a great difference in operating. The army in the enemy's country takes under its protection the organisation which, as it advances, it necessarily introduces to form its lines of communication; and in general, inasmuch as terror, and the presence of an enemy's army in the country invests these measures in the eyes of the inhabitants with all the weight of unalterable necessity, the inhabitants may even be brought to regard them as an alleviation of the evils inseparable from war. Small garrisons left behind in different places support and maintain this system. But if these commissaries, commandants of stations, police, fieldposts, and the rest of the apparatus of administration, were sent to some distant road upon which the army had not been seen, the inhabitants then would look upon such measures as a burden which they would gladly get rid of, and if the most complete defeats and catastrophes had not previously spread terror throughout the land, the probability is that these functionaries would be treated as enemies, and driven away with very rough usage. Therefore in the first place it would be necessary to establish garrisons to subjugate the new line, and these garrisons would require to be of more than ordinary strength, and still there would always be a danger of the inhabitants rising and attempting to overpower them. In short, an army marching into an enemy's country is destitute of the mechanism through which obedience is rendered; it has to institute its officials into their places, which can only be done by a strong hand, and this cannot be effected thoroughly without sacrifices and difficulties, nor is it the work of a moment—From this it follows that a change of the system of communication is much less easy of accomplishment in an enemy's country than in our own, where it is at least possible; and it also follows that the army is more restricted in its movements, and must be much more sensitive about any demonstrations against its communications.
But the choice and organisation of lines of communication is from the very commencement subject also to a number of conditions by which it is restricted. Not only must they be in a general sense good high roads, but they will be the more serviceable the wider they are, the more populous and wealthy towns they pass through, the more strong places there are which afford them protection. Rivers, also, as means of water communication, and bridges as points of passage, have a decisive weight in the choice. It follows from this that the situation of a line of communication, and consequently the road by which an army proceeds to commence the offensive, is only a matter of free choice up to a certain point, its situation being dependent on certain geographical relations.
All the foregoing circumstances taken together determine the strength or weakness of the communication of an army with its base, and this result, compared with one similarly obtained with regard to the enemy's communications, decides which of the two opponents is in a position to operate against the other's lines of communication, or to cut off his retreat, that is, in technical language to turn him. Setting aside all considerations of moral or physical superiority, that party can only effectually accomplish this whose communications are the strongest of the two, for otherwise the enemy saves himself in the shortest mode, by a counterstroke.
Now this turning can, by reason of the double signification of these lines, have also two purposes. Either the communications may be interfered with and interrupted, that the enemy may melt away by degrees from want, and thus be compelled to retreat, or the object may be directly to cut off the retreat.
With regard to the first, we have to observe that a mere momentary interruption will seldom have any effect while armies are subsisted as they now are; a certain time is requisite to produce an effect in this way in order that the losses of the enemy by frequent repetition may compensate in number for the small amount he suffers in each case. One single enterprise against the enemy's flank, which might have been a decisive stroke in those days when thousands of bread-waggons traversed the lines of communication, carrying out the systematised method then in force for subsisting troops, would hardly produce any effect now, if ever so successful; one convoy at most might be seized, which would cause the enemy some partial damage, but never compel him to retreat.
The consequence is, that enterprises of this description on a flank, which have always been more in fashion in books than in real warfare, now appear less of a practical nature than ever, and we may safely say that there is no danger in this respect to any lines of communication but such as are very long, and otherwise unfavourably circumstanced, more especially by being exposed everywhere and at any moment to attacks from an insurgent population.
With respect to the cutting off an enemy's retreat, we must not be overconfident in this respect either of the consequences of threatening or closing the enemy's lines of retreat, as recent experience has shown that, when troops are good and their leader resolute, it is more difficult to make them prisoners, than it is for them to cut their way through the force opposed to them.
The means of shortening and protecting long lines of communication are very limited. The seizure of some fortresses adjacent to the position taken up by the army, and on the roads leading to the rear—or in the event of there being no fortresses in the country, the construction of temporary defences at suitable points—the kind treatment of the people of the country, strict discipline on the military roads, good police, and active measures to improve the roads, are the only means by which the evil may be diminished, but it is one which can never be entirely removed.
Furthermore, what we said when treating of the question of subsistence with respect to the roads which the army should chose by preference, applies also particularly to lines of communication. The best lines of communication are roads leading through the most flourishing towns and the most important provinces; they ought to be preferred, even if considerably longer, and in most cases they exercise an important influence on the definitive disposition of the army.