Dennis H. Mahan

   Dennis H. Mahan was Professor of Tactics and Engineering at the United States Military Academy, during the 1830s and 1840s.  While Mahan is better known for his writings for the application of engineering and fortifications to the art of war, his writings and classes included discussion of tactics and techniques for the maneuvering of small bodies of troops.  His students included some famous names of the American Civil War such as George McClellan, Joe Johnson, and Robert E. Lee.  What is not common knowledge are the thoughts and subsequent teachings from one of his first works about offensive maneuver. D.H. Mahan wrote "An Elementary Treatise on Advanced -Guard, Out-Post, and Detachment Service of Troops and the Manner of Posting and Handling Them in the Presence of an Enemy."  This manual was written by Professor Mahan in his early years at West Point (1837) before earthworks and fortifications dominated his writings and theory. There are seven chapters in this manual which covers the following: -Manner of Placing & Handling Troops; -Positions, Advanced-Guard and Advanced-Posts; -Reconnaissance; -Detachments; -Convoys; and Surprises & Ambuscades.  These chapters deal with regimental tactics and primarily small unit tactics which are not handled well at tacticals and rarely, if at all, at reenactment events. I believe this manual supports the use of small unit tactical concepts we can employ at tacticals. I've only included excerpts from Chapter V and VI for our purposes. If you wish to read the full manual, click on this link Mahan Outpost.

Dennis H. Mahan









Professor of Military and Civil Engineering, and of the Science of War,
in the United States Military Academy







ENTERED according to Act of Congress in the year 1847, by




In the Clerk's Office of the District Court of the Southern

District of New York.





  THE suggestion of this little compilation originated in a professional intercourse, some months back, with a few intelligent officers of the Volunteer Corps of the city of New York. The want of a work of this kind has long been felt among our officers of Militia generally, as English military literature is quite barren in systematic works on most branches of the military art, especially so on the one known among the military writers of the Continent as La Petite Guerre, or the manner of conducting the operations of small independent bodies of troops; and but few of these officers are able to devote that time to military studies, which their pursuit in a foreign language necessarily demands. In making this compilation, the works in most repute have been carefully consulted, and a selection made from them of what was deemed to be most useful to the class of readers for which it is intended.  The object of the writer has been to give a concise but clear view of the essential points in each of the subjects introduced into the work; if he has succeeded in this, he trusts that the very obvious defects of the work will be over­looked. An acknowledgment is here due from the writer to Major-General Sandford, commanding the First Division of the New York State Militia, and to H. K. Oliver, Esq., Adjutant-General of the State of Massachusetts, as well as to the officers generally of the First Division N. Y. S. M., for their kind aid in bringing forward the work.



October 19th, 1847.





CHAPTER I. - TACTICS   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . ..  32




CHAPTER III. - POSITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .    63




CHAPTER V. - RECONNASANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105


CHAPTER VI. - DETACHMENTS . . . . . . .  . . . . . . . . . . . . . . . . . . . .  . . . 117


CHAPTER VII. - CONVOYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  .155


CHAPTER VIII. - SURPRISES AND AMBUSCADES   . . . . . . . . . . . . . . .165


Excerpts of Manual






292. There are no more important duties, which an officer may be called upon to perform, than those of collecting and arranging the information upon which either the general, or daily operations of a campaign must be based.  For the proper performance of the former, acquirements of a very high order, in the departments of geography and statistics, are indispensable requisites; to which must be added a minute acquaintance with topography, and a good coup d'eoil militaire for that of the latter.


293. However detailed and perfect may be a map, it can never convey all the information that will enable an officer to plan, even an ordinary march, with safety; still less, operations that necessarily depend, for their success, upon a far greater num­ber of contingencies.  To supply these deficiencies of maps, an examination of the ground must be made by the eye; and verbal information be gained, on all the points connected with the operation over this ground.  This examination and collection of facts is termed a Reconnaissance.


294.  From the services demanded of a reconnoitering officer, it is, in. the first place, evident, that he should possess acquirements of no ordinary character; but in addition to these he should be gifted by nature with certain traits, without which his acquisitions would be of little account, in the discharge of the responsible duty in question.


295.  With clear and specific information before him, one-half of a general's difficulties, in planning his measures, are dissipated.  In a letter from General Washington to Major Tallmadge, now to be seen framed in the office of the Commissary-General of New York, he remarks, in relation to reports made to him, on a certain occasion: "But these things, not being delivered with certainty, rather perplex than form the judgment." It is in truth this feeling of certainty that constitutes all the difference; having it, the general makes his dispositions with confidence; without it, he acts hesitatingly; and thus communicates to others that want of confidence felt in his own mind.


296.  An officer then, selected for the duty in question, should be known to be cool-headed and truthful; one who sees things as they are, and tells clearly and precisely what he has seen.   In making his report, whether verbally or in writing, the officer should study conciseness and precision of language.  He must carefully separate what he knows, from his own observation, from that which he has learned from others; and add all the circumstances of place, and time, with accuracy.


297. Duties of Reconnoitering Officer.  The first thing to be done by an officer, selected for a reconnaissance, is to ascertain precisely the duty required of him; and what further should be done in case of certain contingencies that may, from the nature of the duty, be naturally looked for.  In the performance of the duty assigned him, and in making his report, the officer should keep always in mind the specific character of his mission, as his guide in both points.


298. As the need of a reconnaissance supposes a deficiency in information upon the features of the country, the officer, detailed to make one, should provide himself with maps, a good telescope, such simple aids for judging of distances, and ascertaining the relative distance of objects, as he can himself readily make; writing materials; one or more good guides; and gain all the knowledge he can, upon his mission.


299. The talent of judging of distances, and of the connection between the various features of a country within the field of vision, is partly a natural and partly an acquired one.  Some individuals can never be brought to have any confidence in their own judgment on these points; others have a natural aptitude for them, which requires but little practice for their perfect development.  The powers of the eye vary so greatly among civilized persons, that no general rules can be laid down, as a guide for the matter in question.  Among uncivilized hordes, used to a roaming life, there are found standards which are well understood by all, - the Arab, for instance, calling that distance a mile, at which a man is no longer distinguishable from a woman growing out of their habits.


307. Reconnaissance.  To designate all the objects to be embraced in a reconnaissance, would lead farther than the limits of this little work will allow; some general heads, which will serve as guides in all cases, will therefore be alone noticed.


308. A general view of the ground to be examined must first be taken in, so as to obtain some notion of the forms of the parts, their connection, and relations to each other, before going into a detailed examination.  To one possessed of some topographical knowledge, this study of what is before him will not demand much time.  A level country, for example, he knows is usually well cultivated, and therefore has plenty of hedges, ditches, &c., which lend themselves well to affairs of light troops, - may be not a little inconvenient to maneuvres of artillery; - and frequently bring up cavalry very unexpectedly in full career.  In a mountainous one, dangerous passes, narrow roads, torrents with rough beds, ugly sudden turns, &c., will necessa­rily be met with.  Each and all of these demand a particular examination, and in his report their ad­vantages and disadvantages should be clearly pointed out by the officer.


309. If the reconnaissance is for an onward movement; the distances from halt to halt, as well as all others, should be estimated in hours of march; the nature of the roads, and the obstacles along them be carefully detailed; the means that may be gathered along the line to facilitate the movement, as vehicles, men and materials for removing ob­stacles, &c.  The points where crossroads are found, must be specified; the direction of these roads; their uses, &c.


310. All local objects along the line. as villages, farm-houses, &c., should be carefully designated, both as to their position on the line, or on either side of it; and also as to their form, and color, &c., as "square white house on the right;" "round gray stone tower on hill to left."


311. The names of localities, in the way in which the inhabitants pronounce them, should be carefully written, and called over several times, so as to be sure to get them as nearly as practicable right in sound; then the names, as written by an intelligent inhabitant, should be added


312. All halting points must be well looked to their military capabilities, in case of attack; as well as their resources for accommodating the troops, be thoroughly gone into. If the halt is to take position for some time, to await or watch the enemy, then more care must be taken, the whole site be well studied as to its fulfill in the proposed end; the points of support on the flanks be designated, as well as others in front and rear, that may require to be occupied; the suitable localities to be chosen for parks, hospital, &c. ; the communications to be opened or repaired, pointed out; and all the facilities either for an advance or a retrograde movement, be laid down.


317. Patrols.  Patrols are of two classes, from the different objects had in view.  The first are those made with a view of insuring greater security from the enemy's attempts to pass, or force the line of out-posts, and may therefore be termed defensive patrols.  They consist usually of three or four men, who go the rounds, along the chain of sentinels and between the posts; seldom venturing farther than a few hundred paces beyond the sentinel's chain; the object being to search points which might pre­sent a cover to the enemy's scouts, and to keep the sentinels on the alert.


318. The second class are those made exterior to the line of out-posts, with a view of gaining intelligence of the enemy's whereabouts; and may therefore be termed offensive patrols. They are composed of larger bodies of men then the first class, the number being proportioned both to the distance to be gone over, and the extent of front to be examined. From the information obtained, through the ordinary channels of maps, and by questioning the inhabitants at hand, the commanding officer can usually settle, with sufficient accuracy, the strength of a patrol.


320. The main duties of a patrol are to find the enemy if in the neighborhood; gain a good idea of his position and strength; to make out his movements, and to bring in an accurate account of his distance from the out-posts of their own force; and the character of the ground between the position occupied by the respective forces.


321. From the nature of these duties, it is evident that both officers and men, for a patrol, should be selected with especial reference to their activity, intelligence, and the aptitude they may possess, from previous habits of life, for a service requiring a union of courage, prudence, and discriminating observation - usually to be met with only in individuals who have been thrown very much upon their own resources.  When the character of the country admits of it, the employment of such individuals, singly, or in very small bodies, as scouts, is one of the most available means of gaining intelligence of an enemy, without betraying the secret of our own whereabouts.


322.       Duties of Officer in command of a Patrol.  In conducting a patrol, the commanding-officer should provide himself with a good map, telescope, and guides; and gain all the information he can before starting, by questioning persons in the neighborhood.  Nothing should escape his eye along his line of search; and he should particularly note points which might be favorable to his defence, if driven back by enemy; or by which his retreat might be endangered.


323.  The order of march of the patrol will be regulated by the circumstances of its strength, kind of troops employed, the character of the country passed over, the hour of the day, and the particular object in view.  The intelligence and judgment of the officer in command will have sufficient exercise on these points; as he will be continually called upon to vary his dispositions.  The general and obvious rule of keeping a look-out on all sides, will prompt the general disposition of an advanced­guard, rear-guard, and flankers, according to the circumstances of the case, however small his command.  The sole object being to carry back intelligence of the enemy, no precautions should be omitted to cover and secure his line of march, without making however, too great a subdivision of his force.


324. Too much circumspection cannot be shown in approaching points favorable to ambuscades; as woods, ravines, defiles, enclosures, farm-houses, villages, &c.  The main-body should always be halted, in a good position beyond musket-shot, or where cover can be obtained, whilst a few men proceed cautiously forward, following at some distance in the rear of, but never losing sight of each other, to examine the suspected spot.  If the officer deem it necessary, at any point, to detach from his command smaller patrols, to examine points at some distance on his flanks, he should halt the rest, at the point where they separate, until the detachments come in and report; or, if he decides to move forward, he should leave three or four men at the spot, to convey intelligence promptly to the rear, if anything is discovered, as well as to himself.


325. It may frequently be found that some eminence on the flanks may present a good view of the surrounding country, in which case, if it be decided to use it, two or three men ought to be detached for the purpose, with orders to keep in sight of each other, but far enough apart to guard against a surprise of the whole.


326.  When the officer finds himself in the presence of the enemy, he should halt his command at a convenient spot, where they will be screened from the enemy's view; and, having made his dispositions against a surprise, he will proceed with a few picked men to the most favorable point from which he can obtain a good look-out, to reconnoitre the position occupied, and the other points of interest.  If he deem it advisable to keep his position, or change it for some other point more favorable, he will first transmit a report to the rear of what he has observed.


327. When the patrol moves by night, the ordinary precautions must be redoubled.  Signals must be agreed upon to avoid danger, should any of the party become separated from the main body.  Careful attention must be given to everything passing around; as the barking of dogs, noises, fires, &c.  On approaching any inhabited spot, the command should be brought to a halt, whilst a few picked men move noiselessly forward, and if practicable, by stealing up to the windows, learn the character the inmates.


328.  It cannot be too strongly impressed upon the mind of the officer in command of a patrol, that be must be all ears and eyes; that he will be called upon in turn, to exercise great boldness, caution, presence of mind and good judgment, in accom­plishing a mission where the enemy must be seen but not encountered; and such roads and halting points be selected, both in moving forward and returning, as shall be most favorable to his movements, and least liable to expose him to a surprise, or a disadvantageous collision with the enemy.







329. Detachments consist of small bodies of troops, composed of one, or several arms, to which are entrusted some mission connected with the operations of the mainbody, but, for the most part performed beyond the sphere of its support; such, for example, as the occupation of some post, or defile, which is to be held temporarily, as necessary to the movements of the mainbody; the surprise of a post held by the enemy; the seizure of a convoy, &c.


330. The composition of a detachment will depend upon the nature of the duty to be performed; the character of the country in which it is to operate; the distance of the point to be reached; and the more or less celerity required in the operation.  As a general rule, detachments should be formed only of light troops, well acquainted with their duties; and, in every case where it can be done, they should consist of a proper proportion of each arm of the service, if the duty upon which they are sent is at all of an important character.  By this combination each arm is enabled to act with more boldness and vigor, from the support with which it will meet in the others; and can better select its moment for action, according to the character of the ground on which it finds itself.


331. The combats of detachments will be mostly restricted to firing, and the skillful employment of skirmishers.  The troops must be kept perfectly in hand for mutual support, the artillery keeping near the infantry, and the cavalry, whenever the opportunity is presented, hazarding only short but vigorous charges against the enemy.


332. The officer placed in command of a detachment, should be thoroughly conversant with the handling of troops; so as to insure constant reciprocity of support; and to be able to seize upon those opportunities of bringing the proper arm into action, and for passing from the defensive to the offensive, which combats between small bodies of troops so frequently present.


333. March of Detachments.  As a detachment must rely mainly on its own resources, the personnel and materiel of the troops should be rigidly inspected before marching; to see that the men and horses are in a sound state; that nothing is wanting in their equipments; that the gun and other carriages are in good traveling order; and that the necessary amount of ammunition, provisions, and forage have been provided for the expedition.


334. Every source of information should be consulted with respect to the nature of the roads, and the country over which the column is to march; and good maps, telescopes, and guides should be provided.  If a reconnaissance of the line of march has been directed, it should be placed in charge of a well informed staff, or other officer, conversant with the duties required of him; so that the commander of the detachment may be accurately informed of the state of the roads, as to their practicability for men, horses, and carriages; particularly the number of hours of march from station to station; and the character of the obstacles with which he may be liable to meet, from the state of the bridges, the nature of the water-courses, and the defiles along the route.


335. In order to avoid being anticipated in our object by the enemy, every attention should be paid to preserve strict order among the troops, and to advance with celerity; so that secrecy maybe kept until the detachment reaches its destination, The troops, for this purpose, should be kept as closely together as the character of the ground will permit; and when the guides are employed, they must be strictly watched, and not dismissed until the march is completed.


336. The distribution of troops, or the order of march, will mainly depend upon the character of the country; the general rule to be followed is so to place each arm in the column, that the troops may be formed for action by the most prompt and simple movements.  In a very open country, the greater part of the cavalry will be at the head of the column; where it is somewhat broken, half of the cavalry may be in front, and the remainder in the rear; and in a very difficult country the infantry will lead.  The artillery may be placed in the intervals of the column where the country is not difficult; in the contrary case it will be in the rear, but covered by a small detachment which it precedes.


337. The column must be secured from a sudden attack of the enemy by an advanced-guard, flankers, and a rear-guard.  The advanced-guard will be composed of cavalry or infantry, or of the two combined, according to the character of the country.  In some cases it may be well to have two or three light pieces with the advanced-guard.  The strength of the advanced-guard, for detachments not over two thousand men, need not be greater than one­fifth of the whole; for larger bodies it may be between a fourth and a third, according to the degree of resistance it may be required to offer.

338. The advanced-guard of a detachment should seldom leave a wider interval than about a thousand paces between it and the main-body.  In a broken country, when this force consists of infantry alone, the distance should be less, to avoid an ambush.  The mainbody of the advanced-guard should always be proceeded by a few hundred paces by a strong patrol of cavalry or infantry, to search the ground and secure the advanced-guard from falling into an ambush, or from a sudden attack.


339.  The flankers will consist mainly of a few detachments, which march parallel to the column and a few hundred paces from it, according to the character of the ground; these will throw out a few men, from a hundred to a hundred and fifty paces, on their exposed flank, to keep a vigilant look-out, in that direction, for the enemy.  Occasional patrols may also be sent out on the flanks, when it is deemed necessary to push an examination to some distant point, or to gain a height offering a commanding view of the country.  As the object of the flankers is rather to give timely notice to the mainbody of an enemy's approach, than to offer any serious resistance, the detachments of which they are composed need only consist of a few men.


340. The rear-guard, except in a very broken or mountainous country, which would offer facilities to the enemy for slipping to the rear, need only be a small detachment, placed more to prevent stragglers from falling to the rear than for any other object.


341. Night marches should not be made, except in case of necessity.  When their object is to surprise an enemy, if there be an advanced-guard, it should be kept near the head of the column.  Patrols should be sent forward, with orders to advance with great caution, and not push on too far.  Flying patrols may, if requisite, be kept up on the flanks.  The most exact order and silence should be maintained, and extreme vigilance be exercised to avoid placing the enemy on the alert.