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Commentary on the use of the Advance Guard in March Order

& its Implication for Meeting Engagements in CWOL


At the onset of the Civil War, there had been no general campaign fought by an American armed force since 1847. The war, in this regard was indeed being fought by a bunch of amateurs who learned by the old process of trial and error though there were valuable lessons documented for their use by both American and European sources. In this article, we will examine the writings of Dennis H. Mahan, Professor of Tactics and Engineering at the United States Military Academy, during the pre-war period of the 1830s and 1840s.  While Professor Mahan is better known for his influence in the application of engineering and fortifications to the art of war, his writings and classes included discussion of tactics and techniques for the handling of large bodies of troops.  His pupils included the top names of the American Civil War, George McCellan, Joe Johnson, and Robert E. Lee.  The primary source for this article will be a little known work by D.H. Mahan titled, "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 work was written by Professor Mahan in his early years at West Point (1837) before his growing fixation with earthworks and fortifications dominated his thoughts.  There are seven chapters in this 50 page work which addresses: Manner of Placing & Handling Troops, Positions, Advanced-Guard and Advanced-Posts, Reconnaissance, Detachments, Convoys, and Surprises & Ambushes.  While much of these chapters deal with regimental tactics and below, there are concepts which affect the maneuver of large unit formations.  These ideas plus additional secondary source work about the teachings of Mahan and others in the pre-war United States form the basis for this article.

Lesson Objective.

In this article you will review:

1.  Doctrinal Theory in the Pre-War Period

The majority of time and effort spend in the pre-war American Army was in the patrol and enforcement of "good order" along the expanding western frontier.  The current trend of the use of the Army in the late 20th century in what is now termed support & stability operations is not unique in the annuals of the American Army.  In 1861, the United States Army was a proven constabulary and frontier defense force.  It had fought a number of campaigns against indigenous peoples, quelled revolts or secessionists in limited instances, plus provided the only form of lawfulness in the majority of various United States Territories. The short, successful limited mobilization and campaigns to defeat the Republic of Mexico in the 1846-47 represents the only deviation in a 45 year time-span between the Civil War and War of 1812 that the army wasn't performing frontier and constabulary duties.

It was not surprising that military theory for the planning and pursue of a general war had limited discussion in the American army.  Fighting a general war was not paramount in the "mission set" of the small nation nor its armed forces. At the United States Military Academy at West Point, NY, there was one major exception to this trend.  He was Professor Emeritus  Dennis H. Mahan, Professor of Tactics and Engineering.  As a young man starting his distinguished career at West Point,  Prof. Mahan participated in the post-Napoleonic debate concerning unit organization and maneuver that was raging in the military camps of Europe.  As Prof. Mahan modified his interests to suit the needs of the frontier army, his latter writings concerned the use of fortifications and engineering within campaigns as well as their application for defense of America's open Atlantic seacoast.  His thought in these areas are well known and documented.  What is not common knowledge are the thoughts and subsequent teachings from one of his first works about offensive maneuver,  "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."

While much of the content of this work was influenced by the Napoleonic theorists of the day, Prof. Mahan was considered a follower of the theories of Baron Jomini, this manual was the sole doctrinal work which transcended the application of offensive theory from regimental tactics ( the basic unit of deployment in the inter-war American army) to units of operational impact such as the division.  Additionally, this work assumed that the tactics being described within it were for application against European-style armies and not the indigenous bands that really composed the primary foes of the frontier army. The combination of this work plus the direct influence Prof. Mahan had on his young students due to his lectures makes his concepts of paramount importance to the Civil War era.

2. The Teachings of D. H. Mahan

It is difficult for citizens of the 20th Century, especially Americans who, in this century, have experienced 10 years of global conflict, 7-12 years of various regional conflict, 40+ years of the "Cold War," and the recent 5 years of "humanitarian missions", to comprehend the 15 years of peace prior to the Civil War {or the 30+ years of general peace that preceded that conflict}. Except for the continuing friction along the western frontier, the United States had no need for the Army above the local level. The study of higher level tactics and units above those found in the frontier posts was an intellectual exercise for most officers and not widespread. However, Prof Mahan, true to his genius shown in his successes as a cadet in the 1820s, studied the writings and post-Napoleonic debate of the Europeans of the evolution that warfare had made during the previous two decades.

What Professor Mahan attempted to do in "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" was take the ideas and theory of the Europeans and put them into a usable manual in the English language. Much of what was contained in his "... Treatise on Advanced -Guard ..." was considered basic drill and maneuver but the focus of the work at the regimental level plus its well-written English prose enabled the work to fill a vast gap in military theory on the North American continent.

Per this writing of Dennis Mahan, the organization of a military unit in the field was characterized by its formation into three bodies: the Advanced Guard, the Main Body, and the Reserve.

The size of these formations should be:

The purpose of these formations are:

Also contained in An Elementary Treatise were numerous what is now called "tactics, techniques, and procedures" on the handling of the Advanced Guard, the Main Body, and the Reserve in the pursuit of gaining and maintaining tactical advantage on the battlefield.

3. Application of the Theories of Mahan in CWOL

The teachings of D.H. Mahan have several useful applications to land combat in CWOL. Starting with the simple organization for combat by forming a Advanced Guard, a Main Body, and a Reserve, a player of CWOL lessens the chance for fragmentation of effort and being surprised tactically. Let us look at an example of the use of an Advance Guard in march order in the CWOL:

The Advanced Guard serves a dual purpose here:

  1. It is the advance recon element of the force approaching Salem, FS (Free State of Astoria) to detect enemy security elements, disrupt any traps or ambushes the enemy has lain in the route of march, and to drive-in any enemy pickets or outposts;
  2. It secures the Main Body from introduction by the enemy and prevents disruption of the friendly maneuver.

Assisting the Advanced Guard in its security tasks are small Flank Guard detachments usually of regimental size from the Main Body that guard against infiltration of the march order by enemy cavalry or serve as detection force if the enemy is attempting to execute an attack of the march order from the flank.

Mahan's Courses of Action:

Within his treatise, Professor Mahan outlines two options, or courses of action, that he saw being possible by a unit in march order that comes into contact with a significant enemy force that can not be overcome by the Advanced Guard.

Frontal Attack

The first Mahan option is the unit reinforces the Advanced Guard and conducts an immediate frontal attack on the enemy force. Mahan viewed the key to success in this case being the application of superior force and coordination by the senior commander on the field to achieve violent execution of the attack. Use of the Main Body to achieve this end was expected technique. The illustration below {Mahan's Course of Action #1} shows the execution of a frontal attack from march order.

In CWOL terms, the Main Body moves to reinforce any success achieved by the Advanced Guard, flank the enemy position or apply overwhelming combat power to seize the junction hex of the strategic square being contested. During this frontal attack, the senior commander on the field takes care to isolate the objective, the junction hex, by positioning the Flank Guard detachments to interdict any enemy reinforcements away from the junction hex. The positioning of the Flank Guard detachments must be far enough away from the junction hex that no enemy weapons can bring fires to effect the attack by the Main Body.


The second Mahan option is the unit withdraws. This is usually only done when the Advanced Guard makes contact with a superior enemy force that could defeat both the Advanced Guard and the Main Body. This is a VERY difficult maneuver involving the extrication of the Advanced Guard from combat with a superior force, the establishment of supporting positions by the Flank Guard detachments and the Main Body, and the withdrawal by echelon of the friendly forces from the fires and actions of the superior enemy force. The illustration below shows the intricacies of this maneuver.

The last unit out, usually the Reserve, serving as the rear guard must ready to take catastrophic losses. In CWOL, this level of loss is usually caused by a Main Body element failing to issue the correct order to withdraw in synchronization with the rest. The rear guard is now charged with maintaining security of that "orphan" unit while it attempts to re-issue its march instructions. This delay will usually cost the rear guard severely as the enemy force will be able to close onto it and bring its superior fires to bear on the guard unit.


An alternative not recognized by Mahan is the bypass of a detected enemy force or outpost that would cause the friendly force unacceptable delay in its march. The principles of this maneuver are simple. (view the illustration below, Alternate Course of Action #3 as you read the following steps.)

Attack of Isolated Force

A second alternative not recognized by Mahan is a coordinated maneuver where the friendly unit leaves march order, the senior commander on the field synchronizes the simultaneous fixing of the enemy force by the Advanced Guard, the isolation of the enemy force by the Flank Guard detachments and the Reserve, and a coordinated attack by the Main Body to defeat the enemy force in detail. This course of action would be selected when the detailed defeat/ destruction of the enemy force is required, or, when the friendly force must destroy the enemy force to insure the security of the seized objective ( junction hex). Below is an illustration of this alternative (course of action #4).

Because situations in CWOL rarely happen in a straight head-to-head orientation, the illustration below shows an application of Course of Action #4 where the enemy force is detected by one of the Flank Guard detachments rather than the Advanced Guard. In this case study, the senior commander determines to maintain the contact with the Flank Guard detachment while using the Advanced Guard to isolate the enemy and rushing the Main Body forward to attack the enemy force.

Use of Artillery

As a note on use of artillery in march order, commanders should insure that batteries with the Advanced Guard have as superior range as possible. The ability of Advanced Guard artillery support to engage enemy forces prior to the commitment of its direct fire weapons will better enable the senior commander to avoid decisive contact.

Additionally, the senior commander should endeavor to mass all artillery at the decisive point in the tactical battle. The combat power of these assets will go greatly to assist in the success of any attack if used in mass and not dueling with enemy artillery. 


This concludes the review of the leading thought and analysis of offensive theory within America prior to the ACW. While this article does not hope to be entirely comprehensive it should give the reader an idea of the state of doctrinal theory in 1860.  American military leaders and students were heavily influenced by foreign writers as well.  For a summary of these points, go to Military Theory of the ACW Era.   However, it should be remembered by the reader that Dennis Mahan was a personal instructor for all ACW era officers who attended West Point in the 1830s, 40s, & early 50s.  His influence on military thought in the small, pre-war American army should not be minimized.

This article is not tied directly to one of the lessons contained elsewhere in the War College but it is hoped that applications of these points would be applied in the Campaign Course or in the war planning for CWOL.

Contained in the links below is the Campaign Course which contains the preparation of a campaign plan and the application of that plan at the operational level. If you want to practice the skills and knowledge gained here, contact your national Secretary of War and request a position in the next iteration of the Campaign Course. See the Links supplementing this Lesson section below for more information about the exercise.


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