Was there an explicit three-to-one rule during the ACW for attacking an entrenched position?

A. Roy

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Some historians have written that, during the Civil War, commanders used a rule-of-thumb that an attacker needed at least a three-to-one numerical advantage to attack an entrenched defensive position.

Whether this is really a valid rule is interesting, but my real question is this: Can anyone point to a explicit Civil-War-era statement of this rule in any kind of source contemporary to the war?

I'm researching the use of fortifications during the war and am interested in the value of entrenchments as a deterrent. So what I would love to see is any quote from a Civil War commander, a military manual, a primary source of some kind, even a newspaper, expressly stating that a three-to-one rule (or any other ratio, I guess) was currently in use at the time.

One example of a historian citing this rule is James McPherson in Battle Cry of Freedom (1988). I found two places where he mentions the three-to-one rule:

"And while loose-order tactics occasionally succeeded in carrying enemy lines, they did not restore dominance to the tactical offensive, especially when defenders began digging trenches and throwing up breastworks at every position, as they did by 1863 and 1864. It became a rule of thumb that attacking forces must have a numerical superiority of at least three to one to succeed in carrying trenches defended by alert troops." (Chapter 15, "Billy Yank's Chickahominy Blues." Page 475 in my Kindle version.)

and:

"Ensconced behind the most formidable works of the war, the rebels had taken heart. They proved the theory that one soldier under cover was the equal of at least three in the open." (Chapter 21, "Long Remember: The Summer of '63." Page 632)

McPherson makes this claim. However, I'm not able to find a footnote or reference in his book pointing to any primary source that supports this rule-of-thumb.

Whether this rule is valid or not has been debated, but I'm just wondering whether this three-to-one ratio was really in use during the war, or whether it is a later invention.

Any thoughts?

RockQuarry_Raleigh_Guion1863.png


(Image source: Henry T. Guion, Lt. Col. Eng. and Art'y, CSA. 1863 map of the entrenchments at Raleigh, NC. Detail at the southwest of the ring of fortifications.)

Roy B.
 

lurid

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How else could you breach those fortifications in that era? Dug in armies in that era had all the advantages, especially the Confederates who knew the terrain and had pretty accurate intel. Nowadays, the just carpet bomb those fortifications and perimeters and then send in ground troops, and that alone stymies the time to tactically maneuver and the intel advantage, but it depends how dug in an army is to sweep the fortification. It is absolutely valid, perhaps to the point that 2:1 or 3:1 advantage was not enough depending on how dug in and well built those fortification were in the south.
 

War Horse

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Before R. E. Lee took command of the ANV following Seven Pines, he was known as "The King of Spades." Might tell you a little something about his view of entrenchments...
He was called The King of Spades after his failures in Northern Virginia (Now West Virginia). Those failures were largely due to the complexity of his battle plans and not having the supporting cast to successfully carry them out. Audacity was his middle name.
 

War Horse

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Before R. E. Lee took command of the ANV following Seven Pines, he was known as "The King of Spades." Might tell you a little something about his view of entrenchments...
I will say this. When compelled to entrench no one and I mean no one was better at it than Robert E. Lee. Just look at his entrenchments on the retreat from Gettysburg to Falling Waters. He earned his nick name The King of Spades honestly and many a soldiers life was spared because of it.
 

Zack

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All I could find:

Lincoln to Halleck, September 19, 1863:

“For a battle, then, Gen. Meade has three men to Gen. Lee's two. Yet, it having been determined that choosing ground, and standing on the defensive, gives so great advantage that the three can not safely attack the two, the three are left simply standing on the defensive also. If the enemies sixty thousand are sufficient to keep our ninety thousand away from Richmond, why, by the same rule, may not forty thousand of ours keep their sixty thousand away from Washington, leaving us fifty thousand to put to some other use? Having practically come to the mere defensive, it seems to be no economy at all to employ twice as many men for that object as are needed. With no object, certainly, to misle[a]d myself, I can perceive no fault in this statement, unless we admit we are not the equal of the enemy man for man. I hope you will consider it.”

https://quod.lib.umich.edu/l/lincoln/lincoln6/1:963?rgn=div1;view=fulltext

This implies but does not explicitly prove the existence of a 3:1 rule.
 

Coonewah Creek

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I will say this. When compelled to entrench no one and I mean no one was better at it than Robert E. Lee. Just look at his entrenchments on the retreat from Gettysburg to Falling Waters. He earned his nick name The King of Spades honestly and many a soldiers life was spared because of it.
I would totally agree that Lee preferred to take the offensive whenever the opportunity arose. His understanding of the strength of an entrenched defense, I think, allowed him to use that knowledge to neutralize a large portion of the strength of the Union army and use the balance of his forces offensively in a (hopefully) surprising way, or as you put it, audaciously...
 

major bill

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This is an interesting question. In modern training a 3 to 1 advantage in combat power is needed by the attacker. This does not require 3 to 1 advantage in the number of soldiers. Also the attacker only needs a 3 to 1 advantage in combat power at the decision point. Many factors go in to figuring out the combat power of the attacker and the defender. I am not sure if during the Civil War era the 3 to 1 "rule" applied to the number of soldiers or the relative combat power of the attacker and defender.

For example, say a Civil War era general sees he has a three to one advantage in soldiers so he attacks an entrenched position. But what if due to muddy roads the attacking general had to leave his artillery behind and the entrenched defenders are well supplied with artillery? The attack will likely fail even if the attacking general has a 3 to 1 advantage in the number of soldiers. The attack might fail if the attacker had a 4 or 5 to 1 advantage in the number of soldiers. This is because artillery is a combat multiplier.

Another example, say an attacking general does not have a 3 to 1 advantage in soldiers but has discovered that the defenders are very low on ammunition. The attacking general probably does not need a 3 to 1 advantage in soldiers if the defenders are low or out of ammunition. In this case a lack of ammunition is a combat power multiplier.

Training, combat experience of the soldiers involved, loss of key leaders, morale, and many other factors are combat multipliers.
 

Eric Calistri

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Location
Austin Texas
Some historians have written that, during the Civil War, commanders used a rule-of-thumb that an attacker needed at least a three-to-one numerical advantage to attack an entrenched defensive position.

Whether this is really a valid rule is interesting, but my real question is this: Can anyone point to a explicit Civil-War-era statement of this rule in any kind of source contemporary to the war?

I'm researching the use of fortifications during the war and am interested in the value of entrenchments as a deterrent. So what I would love to see is any quote from a Civil War commander, a military manual, a primary source of some kind, even a newspaper, expressly stating that a three-to-one rule (or any other ratio, I guess) was currently in use at the time.

One example of a historian citing this rule is James McPherson in Battle Cry of Freedom (1988). I found two places where he mentions the three-to-one rule:

"And while loose-order tactics occasionally succeeded in carrying enemy lines, they did not restore dominance to the tactical offensive, especially when defenders began digging trenches and throwing up breastworks at every position, as they did by 1863 and 1864. It became a rule of thumb that attacking forces must have a numerical superiority of at least three to one to succeed in carrying trenches defended by alert troops." (Chapter 15, "Billy Yank's Chickahominy Blues." Page 475 in my Kindle version.)

and:

"Ensconced behind the most formidable works of the war, the rebels had taken heart. They proved the theory that one soldier under cover was the equal of at least three in the open." (Chapter 21, "Long Remember: The Summer of '63." Page 632)

McPherson makes this claim. However, I'm not able to find a footnote or reference in his book pointing to any primary source that supports this rule-of-thumb.

Whether this rule is valid or not has been debated, but I'm just wondering whether this three-to-one ratio was really in use during the war, or whether it is a later invention.

Any thoughts?

View attachment 409139

(Image source: Henry T. Guion, Lt. Col. Eng. and Art'y, CSA. 1863 map of the entrenchments at Raleigh, NC. Detail at the southwest of the ring of fortifications.)

Roy B.


Have you checked out Dennis Hart Mahan? Perhaps _Summary on the Cause of Permanent Fortifications and of the Attack and Defense of Permanent Works_. He was "the guy" at West Point in the decades before the civil war.
 

Zack

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Have you checked out Dennis Hart Mahan? Perhaps _Summary on the Cause of Permanent Fortifications and of the Attack and Defense of Permanent Works_. He was "the guy" at West Point in the decades before the civil war.

here’s the full text:
https://books.google.com/books?id=6...hUKEwjU3L3lnvrxAhWRhJ4KHUp1Dv4QuwUwAXoECAcQBw

I searched the text for key words to see if I could find anything without luck. Doesn’t mean it’s not in there, just that my lunch break ended. Link above if someone else also wants to look through it.
 

Mdiesel

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Joined
Sep 28, 2010
Location
Maryland
Some historians have written that, during the Civil War, commanders used a rule-of-thumb that an attacker needed at least a three-to-one numerical advantage to attack an entrenched defensive position.

Whether this is really a valid rule is interesting, but my real question is this: Can anyone point to a explicit Civil-War-era statement of this rule in any kind of source contemporary to the war?

I'm researching the use of fortifications during the war and am interested in the value of entrenchments as a deterrent. So what I would love to see is any quote from a Civil War commander, a military manual, a primary source of some kind, even a newspaper, expressly stating that a three-to-one rule (or any other ratio, I guess) was currently in use at the time.

One example of a historian citing this rule is James McPherson in Battle Cry of Freedom (1988). I found two places where he mentions the three-to-one rule:

"And while loose-order tactics occasionally succeeded in carrying enemy lines, they did not restore dominance to the tactical offensive, especially when defenders began digging trenches and throwing up breastworks at every position, as they did by 1863 and 1864. It became a rule of thumb that attacking forces must have a numerical superiority of at least three to one to succeed in carrying trenches defended by alert troops." (Chapter 15, "Billy Yank's Chickahominy Blues." Page 475 in my Kindle version.)

and:

"Ensconced behind the most formidable works of the war, the rebels had taken heart. They proved the theory that one soldier under cover was the equal of at least three in the open." (Chapter 21, "Long Remember: The Summer of '63." Page 632)

McPherson makes this claim. However, I'm not able to find a footnote or reference in his book pointing to any primary source that supports this rule-of-thumb.

Whether this rule is valid or not has been debated, but I'm just wondering whether this three-to-one ratio was really in use during the war, or whether it is a later invention.

Any thoughts?

View attachment 409139

(Image source: Henry T. Guion, Lt. Col. Eng. and Art'y, CSA. 1863 map of the entrenchments at Raleigh, NC. Detail at the southwest of the ring of fortifications.)

Roy B.
I think at least one major handicap is in receiving adequate intelligence regarding enemy numbers. This was often a real problem & how could one definitely know for sure if you out number an enemy 3-1? At some point necessity may dictate your decision to attack, siege or maneuver around an opponent. I believe this is why so many assaults may try to attack at different point of the enemy works… to pin the enemy in place & now allow reenactment along interior lines.

I believe the attackers 3-1 advantage in numbers may gave been theoretically the most opportune scenario but not necessarily the rule of law.
 

Lampasas Bill

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Sep 24, 2018
I can't say for certain, but the three-to-one ratio may be derived from to the writings of Clausewitz, Jomini, Napoleon, or even Frederick the Great. All would probably have been familiar to West Pointers. I suspect that the ratio was based on the number of muzzle-loading weapons it would take to overcome a similarly armed and entrenched opponent. Perhaps someone with time on their hands could track it to one of these theorists.
 

Zack

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Location
Los Angeles, California
Clausewitz

ON WAR

1832

https://www.gutenberg.org/files/1946/1946-h/1946-h.htm



Chapter IX Attack on Defensive Positions

In the book on the defence, it has been sufficiently explained how far defensive positions can compel the assailant either to attack them, or to give up his advance. Only those which can effect this are subservient to our object, and suited to wear out or neutralise the forces of the aggressor, either wholly or in part, and in so far the attack can do nothing against such positions, that is to say, there are no means at its disposal by which to counter-balance this advantage. But defensive positions are not all really of this kind. If the assailant sees he can pursue his object without attacking such a position, it would be an error to make the attack; if he cannot follow out his object, then it is a question whether he cannot manœuvre the enemy out of his position by threatening his flank. It is only if such means are ineffectual, that a commander determines on the attack of a good position, and then an attack directed against one side, always in general presents the less difficulty; but the choice of the side must depend on the position and direction of the mutual lines of retreat, consequently, on the threatening the enemy’s retreat, and covering our own. Between these two objects a competition may arise, in which case the first is entitled to the preference, as it is of an offensive nature; therefore homogeneous with the attack, whilst the other is of a defensive character. But it is certain, and may be regarded as a truth of the first importance, that to attack an enemy thoroughly inured to war, in a good position, is a critical thing. No doubt instances are not wanting of such battles, and of successful ones too, as Torgau, Wagram (we do not say Dresden, because we cannot call the enemy there quite aguerried); but upon the whole, the danger is small, and it vanishes altogether, opposed to the infinite number of cases in which we have seen the most resolute commanders make their bow before such positions. (Torres Vedras.)

We must not, however, confuse the subject now before us with ordinary battles. Most battles are real “rencontres,” in which one party certainly occupies a position, but one which has not been prepared.





Chapter X Attack on an Entrenched Camp

It was for a time the fashion to speak with contempt of entrenchments and their utility. The cordon lines of the French frontier, which had been often burst through; the entrenched camp at Breslau in which the Duke of Bevern was defeated, the battle of Torgau, and several other cases, led to this opinion of their value; and the victories of Frederick the Great, gained by the principle of movement and the use of the offensive, threw a fresh light on all kind of defensive action, all fighting in a fixed position, particularly in intrenchments, and brought them still more into contempt. Certainly, when a few thousand men are to defend several miles of country, and when entrenchments are nothing more than ditches reversed, they are worth nothing, and they constitute a dangerous snare through the confidence which is placed in them. But is it not inconsistent, or rather nonsensical, to extend this view even to the idea of field fortification, in a mere swaggering spirit (as Templehof does)? What would be the object of entrenchments generally, if not to strengthen the defence? No, not only reason but experience, in hundreds and thousands of instances, show that a well-traced, sufficiently manned, and well defended entrenchment is, as a rule, to be looked upon as an impregnable point, and is also so regarded by the attack. Starting from this point of the efficiency of a single entrenchment, we argue that there can be no doubt as to the attack of an entrenched camp being a most difficult undertaking, and one in which generally it will be impossible for the assailant to succeed.

It is consistent with the nature of an entrenched camp that it should be weakly garrisoned; but with good, natural obstacles of ground and strong field works, it is possible to bid defiance to superior numbers. Frederick the Great considered the attack of the camp of Pirna as impracticable, although he had at his command double the force of the garrison; and although it has been since asserted, here and there, that it was quite possible to have taken it; the only proof in favour of this assertion is founded on the bad condition of the Saxon troops; an argument which does not at all detract in any way from the value of entrenchments. But it is a question, whether those who have since contended not only for the feasibility but also for the facility of the attack, would have made up their minds to execute it at the time.

We, therefore, think that the attack of an entrenched camp belongs to the category of quite exceptional means on the part of the offensive. It is only if the entrenchments have been thrown up in haste are not completed, still less strengthed by obstacles to prevent their being approached, or when, as is often the case taken altogether, the whole camp is only an outline of what it was intended to be, a half-finished ruin, that then an attack on it may be advisable, and at the same time become the road to gain an easy conquest over the enemy.





Jomini

ART OF WAR

1838

https://www.gutenberg.org/files/13549/13549-h/13549-h.htm



ARTICLE XXXV.

Of the Attack by Main Force of Fortified Places, Intrenched Camps or Lines.—Of Coups de Main in General.



The tactical measures to be taken in the attack of field-works are few in number. If it seems probable that a work may be surprised if attacked a little before day, it is altogether proper to make the attempt; but if this operation may be recommended in case of an isolated work, it is by no means to be expected that a large army occupying an intrenched camp will permit itself to be surprised,—especially as the regulations of all services require armies to stand to their arms at dawn. As an attack by main force seems likely to be the method followed in this case, the following simple and reasonable directions are laid down:—

1. Silence the guns of the work by a powerful artillery-fire, which at the same time has the effect of discouraging the defenders.

2. Provide for the troops all the materials necessary (such as fascines and short ladders) to enable them to pass the ditch and mount the parapet.

3. Direct three small columns upon the work to be taken, skirmishers preceding them, and reserves being at hand for their support.

4. Take advantage of every irregularity of the ground to get cover for the troops, and keep them sheltered as long as possible.

5. Give detailed instructions to the principal columns as to their duties when a work shall have been carried, and as to the manner of attacking the troops occupying the camp. Designate the bodies of cavalry which are to assist in attacking those troops if the ground permits. When all these arrangements are made, there is nothing more to be done but to bring up the troops to the attack as actively as possible, while a detachment makes an attempt at the gorge. Hesitancy and delay in such a case are worse than the most daring rashness.

Those gymnastic exercises are very useful which prepare soldiers for escalades and passing obstacles; and the engineers may with great advantage give their attention to providing means for facilitating the passage of the ditches of field-works and climbing their parapets.
 

A. Roy

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No, there really was an attacking forces vs an in trenches forces ratio taught at West Point and IIRC 3 to one is very close.
This is interesting to hear. Do you have a reference that confirms that a ratio of this kind was taught at West Point? Even something from a memoir would be a confirmation.

Roy B.
 

A. Roy

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If the enemies sixty thousand are sufficient to keep our ninety thousand away from Richmond, why, by the same rule, may not forty thousand of ours keep their sixty thousand away from Washington, leaving us fifty thousand to put to some other use?

Yes, he's certainly suggesting that fortifications are a force multiplier, if that's the right term. If he's implying a ratio here it looks like 3:2. Partly I'm raising the question here about the purported 3:1 rule-of-thumb because I'm wondering whether this was really a known dictum during the Civil War, or something that emerged later.

Roy B.
 

A. Roy

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Also the attacker only needs a 3 to 1 advantage in combat power at the decision point. Many factors go in to figuring out the combat power of the attacker and the defender. I am not sure if during the Civil War era the 3 to 1 "rule" applied to the number of soldiers or the relative combat power of the attacker and defender.

Yes, you're making some good points here that seem to argue against the existence of a three-to-one rule. It might be a useful conceptual idea, but the realities on the ground are going to be too complex to make this kind of generalization valid. Still, the fact that McPherson and other historians have asserted such a thing makes me wonder where they got it from.

McPherson again, from Battle Cry of Freedom, Chapter 15:

"It became a rule of thumb that attacking forces must have a numerical superiority of at least three to one to succeed in carrying trenches defended by alert troops."

Roy B.
 
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