Chapter V: Rear Guards. Flank Guards

REAR GUARDS.

_Strength and Composition._ A rear guard is practically the inverse of an advance guard, its distribution and arrangements are quite similar. On a forward march (toward the enemy) it is unusual to detail a regular rear guard. The rear organization, without special orders, details a few men to cover the rear. If danger is to be apprehended from the rear as well as the front, a command might have both advance and rear guards. This would be exceptional.

It is in a retreat that a rear guard is of particular importance, especially in the retreat of a defeated force pursued by the enemy. In such a case the rear guard should be made as strong as or even stronger than the advance guard in a forward march. If enemy is pursuing closely, all the available troops still in hand may be used to oppose his advance. Thus a rear guard grades imperceptibly into a delaying force, and its orders may vary from those for a simple march to the occupation of a defensive position, _for delaying action only_. Ordinarily the strength of a rear guard in retreat is about the same as that of an advance guard in a forward march. But as a rear guard, unlike an advance guard, cannot ordinarily count on reinforcements, since the main body is marching _away_ from it, be sure to make it strong enough in the beginning, so that it will not be necessary to detach additional troops to reinforce it.

The rear guard in retreat, usually includes the outpost of the previous night.

Infantry will ordinarily form part of a rear guard, but the proportion should preferably be less than with an advance guard. Infantry has more difficulty in withdrawing from action than mounted troops.

As much cavalry as possible should be assigned to the rear guard, both for reconnaissance and delaying actions. The cavalry should not be independent of the rear guard commander unless the enemy is so far to the rear that touch with him might be lost if cavalry were restricted. A rear guard may well consist entirely of cavalry if there is enough of that arm available.

Motor cars are extremely useful in the pursuit of a defeated force and correspondingly useful in effecting a rapid retreat.

Artillery, especially horse artillery, is extremely useful for delaying the enemy. Hence a rear guard should as a usual thing have artillery. Even a battalion may have a battery or two with it. It is usually concentrated with the reserve.

The conduct of Engineers in a retreat is ordinarily as follows: The engineer company marches with the advance guard or leading troops and prepares bridges for destruction, constructs obstacles, and, if necessary, prepares delaying positions for defense. The mounted section of the engineers accompanies the rear guard and completes the demolitions after all friendly troops have passed. The destruction of bridges is a most efficacious means of delaying the enemy, but care should be exercised not to cut off the retreat of the rear guard cavalry. Also be careful about destroying bridges without the orders of the supreme commander if this might interfere with his plans. It is usually sufficient to merely disable the bridges by removing planking, _if there is time_. If no explosives are available a wooden bridge may be destroyed by fire. The engineers carry explosives. Each squadron of cavalry has also a “demolition squad.”

Machine guns are useful with a rear guard.

Signal troops seldom accompany a rear guard. If present they connect it with the main body.

The field trains of the rear guard usually march with those of the main body in front of all troops in the main column. If with the rear guard they should be sent on well in advance of the reserve--the farther the better--with orders to proceed to some definite point.

Sanitary troops if present with a rear guard should ordinarily be sent ahead of the reserve, but must remain within call in case of need. The artillery combat trains are usually with the sanitary troops, within call. They should not be separated entirely from the rear guard if a serious fight is anticipated.

The fractions of a rear guard are rear cavalry, rear point, rear party, support and reserve. These are analogous to the corresponding fractions of an advance guard, and similarly constituted. Cavalry is employed _tactically_ with a rear guard to a much greater extent than with an advance guard. Hence be cautious about letting it get too much out of hand.

_Distances._ The distances between fractions and from the main body are ordinarily greater than in the case of an advance guard. When the reserve of an advance guard would be 1,000 yards in front of the main body, that of a rear guard might be 1,500 to 2,000 yards in the rear. In the case of a convoy the rear guard usually remains closer (See “Convoys”). The distances of a rear guard cannot be maintained if it has to delay the enemy. It should not become too far separated from the main body, but it may be still more dangerous to be driven in too close.

As the distances are so variable it is not always advisable to prescribe them exactly. If enemy is not in immediate contact, the rear guard may be ordered to follow the main body at a certain distance. Otherwise it may be ordered to “follow delaying the enemy,” or to “march at such an hour,” or in the extreme case the supreme commander may merely inform the rear guard commander of the hour at which the main body will start, leaving the conduct of the rear guard entirely to its commander. It is, however, entirely proper to direct the rear guard commander in orders, to maintain touch with the enemy by means of patrols and to reconnoiter his flanks.

The rear guard commander should keep himself accurately informed as to the progress of the main body, so that he need not risk his safety any more than necessary. The supreme commander should, from time to time, advise the rear guard commander as to the progress of the main body, etc.

_Conduct._ As the column is usually withdrawing from the enemy the reconnaissance of a rear guard is different from that of an advance guard. It seeks to establish contact with the enemy, not only with his advance troops but with his _main body_, and to maintain it as long as possible. Its special duty in the way of reconnaissance is to cover the rear of the main body, not only on the road by which it is retreating, but on parallel roads, so that the enemy while engaging the rear guard with a portion of his force cannot slip by it on a parallel road and strike the main body, or cut off the retreat of the rear guard. Thus it is important to keep in touch with enemy’s _main body_.

The rear guard should take the main road as soon as possible, and retreat as nearly as practicable straight to the rear, following the main body, and covering it at all times.

Its usual procedure if closely pressed by the enemy, is a series of delaying actions, one portion covering the retreat of another. The special duty of the rear guard commander, in addition to reconnaissance of the enemy, is the selection of suitable delaying positions. These should fulfill as many as possible of the requirements of a defensive position. But as they will usually not be held to a decision, it is both permissible and proper to occupy an extended front in order to deceive the enemy and force him to make a wide detour to turn the position. In case of an unexpected delay to the main body, such as a broken bridge, the rear guard might have to fight to a decision. In such case it might be reinforced, but ordinarily should not expect nor call for help from the main body.

If it is possible to delay the enemy with the artillery and cavalry it is well to put as little infantry as possible into action, since it is difficult to withdraw without loss and confusion.

The rear guard commander should consider several positions along the line of march from which the enemy may be delayed. It is well to make the first stand as far to the front as possible--at the outpost line if this is a good defensive position. Consequently the outpost should not be withdrawn prematurely, especially as this also gives the enemy notice of your intentions if he observes it. Another position must then be selected to cover the withdrawal of the outpost and so on. Each position should be such that its fire will not be masked by any retiring troops. As these will generally retire straight to the rear, positions squarely or obliquely on the flank of the line of retreat or line of enemy’s advance are often advantageous. If one flank is toward the enemy in such cases, it should be secure, and there should be a good getaway--the front edge of a woods, impenetrable for the most part, but having lanes through it is a good place for a flanking position. In retreating from such positions the troops may have temporarily to leave the main line of retreat. They should rejoin as soon as possible, since main body must not be uncovered.

If the enemy can be sufficiently delayed by forcing him to deploy one or more times, this is the safest procedure. Accordingly look for high points along the line of retreat, hills and ridges, which may be utilized by the artillery or for position fire of machine guns, and long range rifle fire.

If it is necessary to make a stand, one determined stand in a good position is usually preferable to several half-hearted ones. You may not be able to deceive the enemy more than once as to your strength. If you have a good position do not leave it as long as it is safe to hang on.

A delaying position should preferably have a broad front, a good screen to conceal strength of troops occupying it, an obstacle in its front and a good getaway.

The instructions to an officer commanding a portion of the rear guard in a delaying position might be about as follows: “Major A, you will take up a position at ______ for the purpose of delaying the enemy’s advance (or to cover withdrawal of such troops from such place). When you are in danger of being cut off, break off the engagement and retire via ______ to ______, where further orders will be given you. Messages will reach me at ______.”

The rear guard should be kept as well in hand as conditions permit. All movements should be as simple as possible and as far as practicable, straight to the rear.

The commander of a rear guard should be allowed great latitude. His defensive measures should seldom be prescribed in advance by the supreme commander.

In his own orders the rear guard commander cannot in any case prescribe more than the first two delaying positions--the rear one to cover the retreat from the most advanced. Additional orders are given verbally as necessity arises, but other delaying positions should be considered in estimating the situation.

If the supreme commander has sent out any special patrols to the rear he should mention this in Par. 1 of his retreat order so that rear guard commander may take notice. He should also at all times keep the rear guard commander posted as to the situation, transmitting to him all information bearing upon his duty.

It is unusual for a rear guard to have a flank detachment. If special protection on the flank is required the supreme commander should generally give orders in regard to this, either detailing a special flank guard, or directing the rear guard to do so. If this has not been done the rear guard commander must consider whether his mission _requires_ a flank guard. Apply the rules given under “Flank Guards.” You will then _usually_ find that a flank guard is not required. Moreover it is properly, as stated, the duty of the supreme commander to attend to this. If he had wanted a flank guard he would probably have said so.

In retreating upon the front of a defensive position a retiring force should draw off to a flank or retire into an interval in the line, so as to avoid masking the fire of the position, while at the same time drawing the enemy across the front of the position in such a manner as to subject him to its fire. Consider which flank it is better to approach.

A rear guard must not take the offensive without _special_ orders from the supreme commander, unless necessary for the accomplishment of its mission. In this respect it differs from an advance guard. There will be occasions, however, when aggressive action will best serve to delay the enemy. If the pursuit be conducted too recklessly opportunity for an effective counter-stroke may be presented. In a critical case the supreme commander may himself remain with the rear guard. This would not be usual.

Rear guard orders, in general, are quite similar to those of an advance guard.

A RETREAT ORDER.
Detch., 2nd Div., 1st Blue Army Corps,
TWO TAVERNS, PA.
Field Orders, } 28 Nov., 1912--10:00 p. m.
No. -- }
Gettysburg-Antietam 3" Map.

1. The enemy has camped on ROCK CREEK near GETTYSBURG and near ROUND TOP. About 1 squadron of Red cavalry is in camp near POWERS HILL, additional Red cavalry is reported near BONEAUVILLE.

Our 1st Division marched this afternoon from GETTYSBURG to NEW OXFORD where it will be reinforced. We also are ordered to join it tomorrow.

2. This detachment marches tomorrow, the 29th inst., to join the 1st Division near NEW OXFORD.

TROOPS

(a) Advance Guard:
Col. C.
3rd Inf. (less 1 bn.)
Tr. A, 1st Cav. (less 2
plats.)
(b) Main Body, in order
of march:
1 Bn., 3d Inf.
1st Bn., 1st L. A. (less Btry.
A, and C. Tn.)
2nd Inf. (less 1st Bn.)
(c) Rear Guard:
Major A.
1st Bn., 1st Inf.
2 plats. Tr. A, 1st Cav.
Mtd. Detch., Co. A, 1st Engrs.
(d) Left Flank Guard:
Col. A.
1st Inf. (less 1st Bn.)
1st Sq., 1st Cav. (less Trs.
A & D)
Btry. A, 1st L. A. (less C. Tn.)
4. Train:
Major B.
1st Bn., 2d Inf.
Co. A. 1st Engrs. (less
Mtd. detch.)
F. Tn.
1st Amb. Co.
C. Tn., 1st Bn., 1st L. A.

3. (a). The advance guard will clear MEYER F. H. at 6:00 a. m. and march via ST. LUKE’S CHURCH on SQUARE CORNER. It will maintain communication with the flank guard and train and establish communication with our 1st Division.

(b). The main body will follow the advance guard at 600 yards.

(c). The rear guard, now on duty as outpost, will remain in position until 6:10 a. m. and will then follow the main body. It will keep touch with the Red troops near ROUND TOP by means of patrols and will reconnoiter the enemy’s right.

(d). The left flank guard will march from M. RUDISH F. H. at 6:00 a. m. on SWEET HOME S. H. It will maintain communication with the rear guard, reconnoiter the HANOVER ROAD and not permit the enemy to advance east of BONEAUVILLE before the command has cleared SQUARE CORNER.

4. The train with escort, in the order named, will form by 5:50 a. m. on the GERMANTOWN--555--WHITEHALL Road with the head of the column at BAIR F. H., and will then march via WHITEHALL--601--MARYSVILLE--IRISHTOWN to REDHILL S. H.

5. Messages to the head of the main body.

A,
Brig. Gen.

Dictated to officers designated to receive. (Append list of organizations, see previous order.) Report of dispositions to C. G. 1st Div. by wire.

NOTE:--In this case the detachment is _not required to delay the enemy’s advance_ but only to make good its own retreat. The enemy is not in contact with its outposts. If a serious rear or flank guard action were anticipated it might be better to place all the artillery with the rear and flank guards and the combat trains at the tail of the main body.

If, in a retreat, the enemy is pressing closely it may not be possible to conduct an uninterrupted march, and orders for same cannot be given in advance. In such a case it is often necessary to delay the enemy in successive positions, which duty may be assigned to the rear guard alone, or to the entire force. The rear guard commander, if charged with this duty, will then issue orders for a position in readiness prepared either to reinforce the outpost (which in such a case should have been placed under his command), cover its withdrawal, or take up the march in rear of the main body. Subsequent orders (for a delaying action, another position in readiness, or for taking up the march) may then be issued as the occasion demands. (See “Position in Readiness.”)

FLANK GUARDS.

_Strength and Composition._ No rules can be given for the strength of a flank detachment, as this depends on circumstances to a greater extent than in cases of advance and rear guards. Its limiting strength is about ½ that of the body which sends it out, which amounts to a movement in two columns, and it varies from this maximum down to a mounted patrol, which of course would not be called a flank guard. A flank guard proper is a body which has _some power of resistance_.

A flank guard should generally have a large proportion of cavalry. It may well consist entirely of this arm if there is enough for the purpose, or if a determined resistance is not likely to be required. But if there is paucity of cavalry, not enough to have sufficient resisting power, then infantry should be sent to support the cavalry. As a rule a _special_ flank guard is detailed only when resistance is necessary, hence it will ordinarily consist of infantry and cavalry.

Artillery as a rule does not accompany a flank guard, especially if the situation is such that the artillery from the main body can be thrown over to the flank in case of need. But if the flank guard has sufficient strength artillery may be attached if there appears to be an actual need of it. With a cavalry flank guard horse artillery if available should preferably be used.

Mounted men and machine guns are useful with a flank guard. Engineers, signal and sanitary troops are usually not required.

There should be no wagons with a flank guard, except the regular combat trains. In a flank march the trains should be closed upon the main body, or sent on another road (on unexposed flank) with an escort if required. The trains of the flank guard would be with those of the main body. Ordinarily the wounded or footsore infantrymen riding on the wagons (in addition to the personnel which regularly accompanies them) are sufficient escort for the trains. Do not send the wagon train over a bad road. It is slow enough at best, and on a bad road might, by its slow progress, defeat the very object for which it was separated from the main body. If engineers accompany the command they may be sent with the train to facilitate its progress by repairing bridges, etc. They, of course, also act as escort. In the U. S. field trains can seldom travel in double column, as the roads are not sufficiently capacious.

In a flank march the advance guard (of the main body) need seldom be as strong as in a forward march.

_When required._ A flank guard is not a matter of course like an advance guard. It should be used only when the situation demands it. In deciding whether or not to use a flank guard and if yes what troops to assign thereto, ask and answer the following questions:

1. Is there a hostile force on the flank so strong and so close that it might strike the flank of the column during the march? Make careful calculations of times and distances and consider what enemy is able to do.

2. Will observation on the flank be sufficient, or is resistance very likely to be necessary?

3. Is a flank guard necessary for safety, does it promise a real advantage, or will it merely disperse the troops without any compensation?

4. Will a flank guard actually facilitate the march, or is it more apt to delay it?

5. Is there a suitable road for the flank guard at about 1½ miles distance, with several crossroads connecting it with line of march of main body?

6. Are there any impassable obstacles between the two routes?

7. Is the flank guard likely to have a serious fight? If yes generally send some infantry.

After answering these questions the decision will usually be that no flank guard is required. If you are in doubt do not send one. It is ordinarily better to keep your troops in hand especially in a small force, and protection on a flank can usually be provided by active mounted reconnaissance.

If the flank guard is very strong as compared to the main body the formation becomes virtually a movement in two columns. This may sometimes be an advantage. It shortens the distance from front to rear, and facilitates deployment to the front, so that it might be used to advantage where a combat is anticipated and position of enemy known. The distance between the two columns should be about equal to the depth of one column (combatant troops only) as this facilitates deployment to the front. The trains should be with the column on the less exposed flank, or better still on a third road with an escort. An infantry flank guard not stronger than a regiment, should seldom be more than 1½ miles from the main body.

The ideal case for the use of a flank guard is where there is a certain point, such as a junction of several roads or a lone bridge over an unfordable stream, through which the enemy is certain or at least extremely likely to pass if he operates against the flank, or a strong position commanding the country through which he must pass even when he is not limited to a single route. In this case the flank guard, in sufficient strength, proceeds rapidly to the critical point and there delays the enemy until the main body including the rear guard if there is one, is clear of all danger. But even in this favorable case observation from some commanding point of the country through which the enemy must pass may be sufficient.

Another case in which a flank guard is often used is where a change in direction of march is executed, especially in the case of a convoy. In this case the whole (or a portion) of the former advance guard, reinforced if necessary, may be pushed out to the former front now become the flank, especially if the enemy is known to be in that direction. Here it may seize a strong position and hold it until the main body is out of danger or, according to circumstances, continue the march on a parallel road. A new advance guard is, of course, required, usually not as strong as the former one.

A convoy, being much more vulnerable to an attack than a body of troops, would usually have a flank guard if any danger was anticipated in the direction of its flank. (See “Convoys.”)

An auto convoy may be accompanied by cavalry, foot troops transported by auto, or by a number of armored cars, suitably disposed as advance and rear guards, and as flank guards on parallel roads. On a good road cavalry cannot always keep pace with an auto convoy of light trucks without retarding the speed of the convoy.

The smaller the force the less apt it is to need a flank guard. A large force is much more apt to need one as it requires more time to prepare to meet an attack. For the same reason the flank guard will generally be farther out. A distance of 1½ to 2 miles is sufficient to protect a column against surprise by artillery fire, and this is ordinarily the _limiting distance_ for a flank guard. A very large flank guard, being more independent and able to stand a longer time without reinforcement, might be farther out. Such a body, however, would be a detachment rather than a true flank guard.

If the flank guard consists entirely of cavalry its distance away, and the matters of communicating roads and obstacles between it and the main body (see ante) are of much less importance than where the bulk of the flank guard is infantry. A strong covering body of cavalry some distance out, however, is virtually independent cavalry and would generally be called such. Its movements would seldom be limited to any particular route.

_Conduct._ A flank guard marches like any other body, with advance guard, rear guard if necessary, and other security measures. This, of course, is not prescribed in the orders to the flank guard, but is left to its commander. A flank guard does not usually put out its own (another) flank guard. If of cavalry it should send officers’ patrols well to the exposed flank, and if of infantry it employs its cavalry or other mounted men to reconnoiter its exposed flank. It is, of course, extremely desirable to gain touch with the enemy.

Unless there is distinctly an independent mission for the cavalry on the flank it is advisable to place the cavalry with the flank guard and under the commander thereof. Otherwise the cavalry is very apt to get out of hand and fail to co-operate with the infantry. If, however, the cavalry commander is also the commander of the entire flank guard, the necessary freedom of action of the cavalry will not be restricted, while at the same time co-operation between the cavalry and the infantry is assured. Therefore if the cavalry with the flank guard is relatively strong (as compared to the infantry) and the relative rank of the officers concerned permits it, the entire flank guard may well be placed under the cavalry commander.

A flank guard should not bring on a decisive engagement unless it is empowered to do so, as this might involve the main body, contrary to the wishes of the supreme commander.

A flank guard usually marches abreast of the main body. The advance guard (of the main body) keeps touch with the flank guard, but the latter should maintain communication with the rear guard (of the main body) and not fail to consider the safety of the latter, as it might be endangered if the flank guard advanced or retired too rapidly, allowing the enemy to cut in.

A flank guard usually will not be reinforced. But this may be necessary for the safety of the main column. Hence the obstacles between the two routes and the roads by which the flank guard may be reinforced in case of necessity, must be carefully considered.

The orders of the supreme commander should ordinarily prescribe the time of departure, route and special mission of the flank guard. After this considerable latitude should be allowed the flank guard commander as his actions will depend to a great extent on those of the enemy. The march of a flank guard will not always be continuous. It must, when necessary, halt in suitable places en route, assuming a defensive attitude if necessary, to delay the enemy until main body is clear. The flank guard commander must consider the enemy’s probable line or lines of advance, and the dispositions he will make to delay him. He will not hesitate to leave the prescribed route of march if his mission demands it. He will keep the supreme commander informed as to his actions, particularly if the enemy is encountered, and call for reinforcements when absolutely required.