RECONNAISSANCE (from Fr. reconnattre, to recognize, Lat. recognoscere), is an examination of a tract of country or of the sea-coast; the latter previously to a discmbarkatiun of troops, and the former preparatory to the march of an army in order either to meet that of the enemy or to take up quarters for the season.
The military reconnaissance of a country is a duty appertaining to the officers on the staff of the quartermaster-general; and if the enemy is in the neighbourhood, it is performed under the protection of an armed force. It is considered as one of the most essential operations connected with the tactics of the field, and serves as the basis of every movement or combination which it may be proposed to make.
A general knowledge of a country which is or may become the seat of war, that is to say, a knowledge of the positions of its fortified places, the directions of its mountains, rivers, and great roads, may be obtained from maps or from geographical descriptions; but that which is necessary for the immediate purposes of a campaign can only be acquired by an actual survey of the ground in detail, and by inquiries made on the spot respecting the means which the country may afford for supplying the wants of the army.
The Marechal Puysegur (1690) appears to have been the first in modern warfare who regularly performed this duty by examining personally the tract through which the army P. C, No. 1208.
was to march or in which it was to encamp, and of deciding beforehand on the best routes and positions. He ob'serves (Art de la Guerre) that before his time it had been customary to trust, for a knowledge of these points, to the reports of the country-people, or of officers who might accidentally have been on the ground. He adds that disasters frequently occurred by the lines of march being improperly chosen, and that sometimes, after fatiguing marches, and after all the labour of encamping Had been undergone, the troops had been compelled to abandon the positions on account of their unfitness. Since that time armies being more numerous and more widely disseminated, consequently requiring more vigilance in the communication of one part with another, and a greater extent of country for their support, the reconnoissances have been made on a greater scale, and in the military establishments of every nation officers are now particularly instructed in all the details of that branch of service.
Those who are charged with this duty should be habituated to the performance of topographical surveys: in the first place by the most accurate methods and with the best instruments; and, secondly, by such methods as admit of being practised rapidly on foot or on horseback. In these cases a compass held in the hand must be used for observing the angles, and the distances must be obtained by pacing, or be merely estimated by the eye. A facility in representing on the plan the inequalities of the ground is also highly necessary.
In making the reconnoissances previously to the march of an army, the whole of the ground between the actual position of the latter and that which is intended to be occupied should be surveyed if the enemy is near aud there is danger of his attacking the columns by surprise; otherwise it may be sufficient to survey the ground within a few hundred paces on each side of the roads by which the columns are to march. A complete plan of the tract of country in which the reconnoissance is made may therefore be required; or it may suffice to represent on paper the line or lines of march. In either case, the officer may be provided with a general map, or an itinerary of the intended route as an outline for his guidance; and his survey, when completed, should be accompanied by a report or memoir, stating in detail what cannot be conveniently represented on the plan. In this report should be expressed, with all necessary references to the plan of the ground, the distances, by the different routes, between the two positions, and the places where troops may halt for repose or to form in order of battle; distinguishing particularly the plains where cavalry may act, and the heights on which artillery may be placed. The nature of the roads should be described, with indications denoting that they are passable for artillery, for cavalry, or merely for infantry; and if defective, estimates should be made of the materials and time requisite for repairing them. It is particularly necessary to state whether the ascents and descents are gentle or abrupt; and, when the road is on the side of a hill, whether it is sufficiently level to allow artillery or carriages to pass safely: it should also be noticed whether or not, at places where roads run through towns, they are reduced to narrow and winding streets. The breadths and velocities of rivers, streams, and canals which cross the lines of march should be ascertained, and a statement made whether the beds are rocky, gravelly, or muddy; also whether the banks are high or low. Mention should also be made of the means which exist for passing them; of the places where they are fordable, where there are ferries or bridges, or where boats may be procured; descriptions should also be given of the bridges or boats, and the manner of working the latter. The situations and extent of marshes should also be shown, and it should be stated whether they are passable or can be made so. In contemplating rivers and marshes as means of retarding an advance of the enemy, it should be ascertained and reported whether, by being dry in summer or frozen in winter, they may not at times cease to be obstacles: it should also be stated how, on a retreat, the roads may be blocked up, the fords rendered impassable, or the bridges destroyed.
Should a sufficient number of roads for the different columns not exist, the officer is to ascertain whether or not others may be made by cutting through hedges, walls, or woods, by forming causeways over marshes, or by constructing or repairing bridges over rivers or streams; and also whether the country affords the materials necessary for these purposes. The rates at which it is possible for troops to march in the several roads, defiles, &c. must be estimated according to the breadth of the latter or the degree of their practicability; for on a right estimate of such rate, together with the known length or the road, depend the number of battalions and the class of troops which ought to be appointed to follow each particular route, when it is required that the different columns should arrive at the same time in some given position. The plan should show the situations of farms, mills, houses, &c. which may be capable of being defended or of affording quarters for the troops; and on it should be indicated, by some scale of numbers or otherwise, the relative heights of the ground, that it may be ascertained what positions can be occupied with advantage for offensive or defensive operations. The representation of a simple line of march should also indicate the places where roads diverge from or cross the route, with the distances of the nearest towns or villages from thence; and any particular survey of the ground for an encampment should extend to at least a mile every way beyond the supposed chain of outposts. [military Positions; Piquet.] The report must state what are the resources of the country in corn, cattle, and forage; and the number of carriages, horses, and other draught animals that it may furnish for the conveyance of artillery and stores. If the line of march is in the direction of a navigable river which may be available for the lastmentioned purpose, it will be necessary to ascertain its breadth and rapidity, and also the obstructions which may be met with from shallows, weirs, &c. Marshal Sin-hut caused his artillery to be conveyed by the Ebro from Mequinenza toXerta, in 1810, preparatory to forming the siege ef Tortosa.
An open country presents the greatest facilities for reconnoitring, since the positions of its towns or villages, and the directions of its roads and rivers, can then be easily distinguished and represented on paper. A tract covered with wood is not only surveyed with difficulty, but it imposes on the officer, in addition, the necessity of ascertaining all the directions in which it is capable of being penetrated by the enemy, and in what manner the passes may be blocked up or defended. Open plains intermingled with wood, fields surrounded by hedges, ground intersected by streams of water, ravines, and hollow ways, demand great exactness in the survey, since such tracts afford the most important advantages, both in the higher and in the secondary operations of warfare, to the army which is best acquainted with their details. They allow troops to pass unseen from one point to another when a surprise is attempted or a rapid retreat is to be made; they also afford cover from whence the enemy may be annoyed with little loss. In mountainous districts it is important to ascertain the forms and directions of the chains of heights, with their acclivities on both sides; and, if the lino of march is between them, the collateral ravines should be examined to a considerable distance: the commencements and directions of the ravines should also be shown, and all the defiles by which the valleys communicate with each other. Through these defiles troops detached from the army are enabled to fall suddenly on the enemy during his march, to separate his columns, and intercept his supplies or cut off his retreat; and, on the other hand, since the enemy may attempt the like measures, it becomes necessary that the officer employed to reconnoitre should ascertain by what means the passes may be barricaded either to impede the enemy or enable the troops to defend themselves.
In reconnoitring a country, when it is intended to act on the defensive, it should be well known by what roads the enemy can penetrate, and where are the best situations for forming intrenched camps or establishing posts in order to be enabled to keep the field and cover the magazines. Again, if it be intended to carry the war into an enemy's country, it is necessary to discover the position occupied by his army; to find the tract of country most proper for the march, and the spots where the localities permit encampments to be formed with due support on the Hanks and security in the rear. If it be intended to besiege a fortress or to attack the enemy's position, the reconnoissance may be made quite up to the glacis of the place, or to the works which protect the position. In the former case it is necessary to ascertain the nature of the fortifications, and the fitness of the ground about them for the operations of the liege; and in the latter, to find out the strength and dispositions of the enemy's troops. An aimed force is generally required on these occasions, as, in order to approach near enough for the purpose, it may be necessary to drive in some of the outposts. During the war which ended in IS) 4. the English and French out-sentries appear to have entertained a mutual understanding not to molest each other, and to retire to their supports before they commenced firing when cither army was about to make a movement. Colonel Napier relates that Lord Wellington, being once desirous of reconnoitring the enemy's position at Bayonne, ordered hit escort to fire upon some of the enemy who occupied the top of a hill which he wished to ascend; but one of the men going up to the French soldiers and tapping his musket is a particular way, the latter, who understood the signal. quietly withdrew.
Ina maritime reconnnnoissane the circumstances which it is of most importance to ascertain are: whether the roast is rocky or bordered by downs, and what is the state of the bays or roads with respect to shelter from the prevailing winds; the seasons in which winds blow off and on the shore, and whether the anchorage is secure or otherwise; the nature of the tides, the hours of high and low water, and the depth at either of those times. Precise information should also be obtained of the places at which troops might land, and where there exist rising grounds on which artillery may be disposed to protect them. Rivers should be ascended to a considerable distance if possible, in order to ascertain their depths and the nature of the vessel* employed on them by the people of the country. On the other hand, if it were required to examine the coast preparatory to putting it in a state of defence, it would be necessary to find out what points of land are convenient for the situations of forts or batteries by which the enemy may he prevented from landing-, and where beacons may be established for the purpose of giving timely alarm. If there are islands on the coast, it would be proper to include them in the survev. since they might be fortified and made to serve as advanced works; and all places should be indicated which are capable of being converted into military posts to prevent the enemy from penetrating into the interior of the country.
Note - this article incorporates content from The Penny Cyclopaedia of the Society for the Diffusion of Useful Knowledge (1840)