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

Zack

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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.
Well he seems to be saying 3:2 is NOT enough, which implies 3:1 is the ideal.
 

A. Roy

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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.

Thanks for pointing to this. I've read his Treatise on Field Fortification, but this other source might mention the kind of ratio approach I'm wondering about. If West Point graduates came away with this concept of a 'three-to-one' rule or something similar, Mahan could well have been the source of it.

Roy B.
 

Rhea Cole

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The ‘rule of thumb’ is derived from English Common Law. A man can only beat his wife with a stick no wider than his thumb. Exactly where that bit of practical advice came from is obscure. I assume it sprang from experience. Everybody knows it means the agreed upon solution without having any notion of its literal meaning or derivation.

The 3 to one ratio at the point of attack rule of thumb is ubiquitous, as well. Even in checkers, it is all but impossible for less than three kinged pieces to pin down & capture one. The same goes with chess. Avalon Hill & other war games tip the advantage to the attacker at three to one. It was no mystery to anybody during the Civil War that a three to one ratio at the point of attack was a winning formula. Their problem was more complicated than that.

During the age of black powder warfare, after firing one shot attackers became pikemen. Repeatedly during the CW a trench line was overwhelmed & the attackers were unable to exploit it to the point of a breakthrough. The lack of communication, mobility & firepower meant that the defender had time to mount a counter attack & seal off the breach. Something else won Civil War battles.

‘A fortress is only as strong as its flanks.’ Is another military truism. Attackers won great victories in CW battles by attacking the opponent’s flank in overwhelming force. Rosecrans won the Battle of Stones River on the third day when he bloodlessly turned Bragg’s right flank & utterly defeated a counter attack. The same was true when he turned Bragg’s flank on a colossal scale during the opening phase of the Tullahoma Campaign.

Thomas’ defeat of Hood at Nashville had the determined attack on entrenched Orchard Knob beaten back on his left allowing time for a flanking attack to overwhelm on the right.

At Shelbyville, during the first day of Tullahoma, Wheeler’s outnumbered force held behind elaborate defenses until flanked. What followed was one of the most lopsided defeats of the war.

The three to one rule of thumb was well established long before the CW. With entrenchment & rifled weapons, the flank attack was the new rule of thumb for overwhelming victory.
 
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A. Roy

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The 3 to one ratio at the point of attack rule of thumb is ubiquitous, as well. Even in checkers, it is all but impossible for less than three kinged pieces to pin down & capture one. The same goes with chess. Avalon Hill & other war games tip the advantage to the attacker at three to one. It was no mystery to anybody during the Civil War that a three to one ratio at the point of attack was a winning formula. Their problem was more complicated than that.

Very interesting. Good point about the importance of the flank attack. So are you thinking that this three-to-one rule was just so commonly held and well-understood during the Civil War that nobody thought they needed to mention it explicitly? (Or nobody that we've been able to identify yet.)

Roy B.
 

Rhea Cole

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Very interesting. Good point about the importance of the flank attack. So are you thinking that this three-to-one rule was just so commonly held and well-understood during the Civil War that nobody thought they needed to mention it explicitly? (Or nobody that we've been able to identify yet.)

Roy B.
It is a good question. My first overnight camp counselor was a chess & checkers master. I was ten. He introduced me to the three to one principle. I almost can't remember not knowing it.

That is why I used the Rule of Thumb in my intro. Everybody knows what it means, nobody has a clue where it came from. Unfortunately, there wasn't actually a manual. There wasn't a War College. There weren't squad tactics manuals. People I have known who were taking a deep dive into CW tactics have found it frustrating for that reason. Afterwards, nobody conceived of fighting a war with an army of a million men, so lessons learned were not documented like we would want them to.

Veteran troops, as Grant observed, would go to ground & not expose themselves making tactically impossible attacks. Another military cliche is that a veteran soldier is a terrified soldier. The men on the ground figured a lot of the CW tactical realities before the generals did. These are, of course, generalities... true never the less. It is reasonable to assume that they understood the three to one at some level.

This puts me in mind of storming a breach in a fortress wall. Victory was achieved by overwhelming the defenders at a narrow point. The attacker had to achieve numerical superiority at the breach, not over the entire garrison. I can't document it right off, but I would not be surprised that our friend the three to one rule of thumb was in play.
 

Irishtom29

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Wellington attacked the three breaches at Badajoz (all in the same stretch of wall: one in a curtain and one in each of the two bastions that flanked it) with two divisions, which were repulsed. However the Brits carried the walls with diversionary attacks at two other spots.
 

Belfoured

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I've never found a source of the 3:1 "rule". It seems to have continued existence in modern military theory as a mathematical concept but I haven't seen any of these discussions specifically identify an origin. If you go back far enough there is evidence that Vauban stated that in a siege the attacking force should have a 6:1 advantage, but I believe that during the F&I/SYW, Montcalm appears to have assumed that 3:1 was adequate in applying Vauban at Fort William Henry.
 

Zack

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Screen Shot 2021-07-25 at 3.21.41 PM.png
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https://apps.dtic.mil/sti/pdfs/AD1083211.pdf


https://www.google.com/books/editio...nco+prussian+war&pg=PA405&printsec=frontcover

Screen Shot 2021-07-25 at 3.24.24 PM.png


It's not in Mahan.
 

Zack

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Earl J Hess wrote a trilogy of books on Field Fortifications during the war if you're interested in that area of study.

Field Armies and Fortifications in the Civil War: The Eastern Campaigns, 1861-1864

Trench Warfare under Grant and Lee: Field Fortifications in the Overland Campaign

In the Trenches at Petersburg: Field Fortifications and Confederate Defeat
 

Zack

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Napoleon's Maxims of War
https://www.gutenberg.org/files/50750/50750-h/50750-h.htm#NAPOLEONS

Excerpts dealing with strength and fortifications.

Maxim X: "When an army is inferior in number, inferior in cavalry, and in artillery, it is essential to avoid a general action. The first deficiency should be supplied by rapidity of movement; the want of artillery, by the nature of the manœuvres; and the inferiority in cavalry, by the choice of positions. In such circumstances, the morale of the soldier does much."

Maxim XIV: "Among mountains, a great number of positions are always to be found very strong in themselves, and which it is dangerous to attack. The character of this mode of warfare consists in occupying camps on the flanks or in the rear of the enemy, leaving him only the alternative of abandoning his position without fighting, to take up another in the rear, or to descend from it in order to attack you. In mountain warfare, the assailant has always the disadvantage; even in offensive warfare in the open field, the great secret consists in defensive combats, and in obliging the enemy to attack."

Maxim XVII: "In a war of march and manœuvre, if you would avoid a battle with a superior army, it is necessary to entrench every night, and occupy a good defensive position. Those natural positions which are ordinarily met with, are not sufficient to protect an army against superior numbers without recourse to art."

Maxim XLI: "If the besieging force is of numerical strength enough (after leaving a corps before the place four times the amount of the garrison) to cope with the relieving army, it may remove more than one day’s march from the place; but if it be inferior in numbers after providing for the siege, as above stated, it should remain only a short day’s march from the spot, in order to fall back upon its lines, if necessary, or receive succor in case of attack.

If the investing corps and army of observation are only equal when united to the relieving force, the besieging army should remain entire within, or near its lines, and push the works and the siege with the greatest activity."

Maxim XLIII: "Those who proscribe lines of circumvallation, and all the assistance which the science of the engineer can afford, deprive themselves gratuitously of an auxiliary which is never injurious, almost always useful, and often indispensable. It must be admitted, at the same time, that the principles of field-fortification require improvement. This important branch of the art of war has made no progress since the time of the ancients. It is even inferior at this day to what it was two thousand years ago. Engineer officers should be encouraged in bringing this branch of their art to perfection, and in placing it upon a level with the rest."
 

A. Roy

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There's a lot to say about this three-to-one rule, but one thing that seems evident is that it's an over-simplification to say that a Civil-War attacking force needed at least three times as many men as the defenders to overtake an entrenched position -- or to say that a three-to-one or greater advantage would be sufficient. The attacker's or defender's head-count is only one factor in the outcome of an engagement.

In spite of that ambiguity, I've run across this rule a few times in the writings of historians, such as McPherson, as I mentioned previously. So I still find myself wondering whether a reference to a rule like that can be found among the writings and communications of Civil War commanders or related primary sources. @Zack pointed to an interesting communication from Lincoln to Halleck that hints at this kind of force ratio -- see Zack's post at https://civilwartalk.com/threads/wa...ng-an-entrenched-position.187467/post-2431348

I did find an apparent reference to the three-to-one ratio (also suggesting four-to-one) in The Photographic History of the Civil War, published in 1911, less than 50 years after the end of the war:

"Grant went East, turning over the command of the Western Federal armies to Sherman, who prepared to attack Johnston, entrenched around Dalton, in northern Georgia. Buzzard's Roost formed the strongest portion of Johnston's line, which consisted of heavy fortifications on the heights, in front of which lighter lines had been placed. Sherman felt this position, found it almost impregnable, made a flank movement, and turned Johnston out of his stronghold. In the retaining attack on the works, the Federal troops took a portion of the lower lines of entrenchments, but found the upper works too strong. The turning movement having succeeded, the Union troops withdrew from the front, and Johnston retired to Resaca, and thence to succeeding positions until Atlanta was reached. Direct assaults on entrenchments nearly always failed with heavy loss.

"By this time it was thoroughly understood that the function of breastworks, whether of earth, logs, rails, or other material, was to give the advantage to the defense, and consequently everyone recognized that good troops behind such protection could hold off three or four times their number of equally good troops making the assault. This was the proportion depended on, and the calculations of the commanding generals were made accordingly. It was usually considered that troops in the works were inferior to the assailants if they did not succeed in withstanding the attack of several times their own strength."


("Entrenchments and Fortifications," O.E. Hunt. In The Photographic History of the Civil War, Francis Trevelyan Miller, ed. Volume 5, "Forts and Artillery." New York: The Review of Books Co., 1911. Pages 208-210.)

O.E. (Ora Elmer) Hunt, the editor of Volume 5 of the Photographic History and author of the "Entrenchments and Fortifications" article, was an army officer and West Point professor. He lived from 1872 to 1969, so his career was post-Civil War. Still, his life and career overlapped with many Civil War commanders, some of whom were contributors to his volume of the Photographic History.

So, although this 1911 source still doesn't provide a citation of the three-to-one rule in a context contemporary to the Civil War, Hunt was in a position to know how commanders thought during the war.

All the same, I'm still hoping to find something explicit on this rule mentioned during the war. CWT members have contributed some great commentary to this question -- much appreciated!

ConfedFortAtlanta_PhotogHistoryVol5_P197.png


(Image credit: Photographic History, page 197)

Roy B.
 

Mark F. Jenkins

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I like Jomini's comment after discussing several historical attacks: "In reading such facts, we must draw from them not rules, but hints; for what has been done once may be done again." I don't think anyone ever laid down an explicit three-to-one rule, since it was so highly dependent on other variables (especially position and terrain).
 

A. Roy

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I like Jomini's comment after discussing several historical attacks: "In reading such facts, we must draw from them not rules, but hints; for what has been done once may be done again." I don't think anyone ever laid down an explicit three-to-one rule, since it was so highly dependent on other variables (especially position and terrain).

This makes sense and could be the reason why I'm not running across any clear articulation of a three-to-one rule in sources contemporary to the ACW. In other words, maybe CW commanders didn't talk about such a rule because they recognized that force comparisons were too complex to be codified merely in terms of how many soldiers stood on each side.

On the other hand, we've seen some comments here suggesting that maybe the rule wasn't mentioned explicitly because it was pervasive and everybody knew about it -- it was just assumed as part of the standard thinking of the time, so nobody thought it needed to be said.

(Note for later reference: Mark's quotation is from Jomini, "The Art of War"; Chapter 4, "Grand Tactics and Battles"; Article 35, "Of the Attack by Main Force of Fortified Places, Intrenched Camps or Lines—Of Coups de Main in General"; page 217.)

Roy B.
 

Belfoured

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This makes sense and could be the reason why I'm not running across any clear articulation of a three-to-one rule in sources contemporary to the ACW. In other words, maybe CW commanders didn't talk about such a rule because they recognized that force comparisons were too complex to be codified merely in terms of how many soldiers stood on each side.

On the other hand, we've seen some comments here suggesting that maybe the rule wasn't mentioned explicitly because it was pervasive and everybody knew about it -- it was just assumed as part of the standard thinking of the time, so nobody thought it needed to be said.

(Note for later reference: Mark's quotation is from Jomini, "The Art of War"; Chapter 4, "Grand Tactics and Battles"; Article 35, "Of the Attack by Main Force of Fortified Places, Intrenched Camps or Lines—Of Coups de Main in General"; page 217.)

Roy B.
That's a good point. Back in the day Vauban was criticized for his 6:1 "rule" because it was too dogmatic/artificial. That may be why Montcalm, for example, used a 3:1 ratio at Fort William Henry in 1757, even though he would have been a disciple of Vauban.
 

67th Tigers

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The ‘rule of thumb’ is derived from English Common Law. A man can only beat his wife with a stick no wider than his thumb.

Well, no. That interpretation was drawn from a satirical cartoon from 1782, and is the 18th century equivalent of reporting an article from The Onion as fact. It was found by legal feminists in the 1970's and used out of context.

To be clear, there was never such a law or principle - it was entirely based on a satire of Francis Buller. This satirical image:

Judge_Thumb.jpg
 
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67th Tigers

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That's a good point. Back in the day Vauban was criticized for his 6:1 "rule" because it was too dogmatic/artificial. That may be why Montcalm, for example, used a 3:1 ratio at Fort William Henry in 1757, even though he would have been a disciple of Vauban.

Montcalm believed he was attacking a force of around 1,300 men rather than the 2,351 men in the fort. A large reinforcing column arrived just before Montcalm (991 men under Lt Col Young, mainly Frye's Massachusetts regiment), and were not accounted for in his planning. He a force of 8,029 men (2,570 metropolitan troops, 542 marines, 2,946 militia, 1,799 Indians, 188 gunners and 2 engineer officers), or a planning figure of approximately 6:1.

Frye's regiment et al. meant he only had a force of 3.4:1, and he adopted regular approaches with his 46 gun artillery park. He did not attempt to assault the works.
 

Belfoured

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Montcalm believed he was attacking a force of around 1,300 men rather than the 2,351 men in the fort. A large reinforcing column arrived just before Montcalm (991 men under Lt Col Young, mainly Frye's Massachusetts regiment), and were not accounted for in his planning. He a force of 8,029 men (2,570 metropolitan troops, 542 marines, 2,946 militia, 1,799 Indians, 188 gunners and 2 engineer officers), or a planning figure of approximately 6:1.

Frye's regiment et al. meant he only had a force of 3.4:1, and he adopted regular approaches with his 46 gun artillery park. He did not attempt to assault the works.
A lot of room for interpretation on that one regarding the "planning figure". Hence my employment of "used".
 
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