Discussion "In support" versus "in reserve"

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I'm looking for clarification of these terms in the context of combat troops in the American Civil War.

It is my understanding that when we say a unit is "in support," that means they are in position to lay down suppressive fire while another unit conducts an assault or any kind of movement that puts them in the line of fire.

A unit it "in reserve" is not actively engaged in combat. They are held back to be placed into the fight when and where they are needed.

I'm I correct in this? Is there more?

Thanks!
 

67th Tigers

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There was no "suppressive fire" at this time. The dense formations and low ROF of the weapons systems didn't allow for it.

A support is a line formed behind the assaulting line ready to exploit or for the assaulters to fall back on if they fail. It is essentially the "second line".

A reserve is well behind that, and a true reserve is a completely uncommitted body of troops free to do anything. If move to support an assault, they are no longer a reserve.
 

Saphroneth

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The reason why a reserve is when a formation is uncommitted is basically related to distance and time. Taking as an example Gettysburg, which is a relatively compact battlefield, the fish-hook is perhaps three miles from north to south.

If the reserve is at (say) the modern visitor's centre and is uncommitted, this means that it's ideally formed up in column and ready to react. Once a message is sent to put them somewhere, the force can move out in relatively short order to any part of the line - given marching speeds over short distances, they can start arriving in perhaps half an hour or a bit more and begin deploying.
If however the reserve is on the left flank and is deployed as a second line, then if they're needed on the right flank or at Cemetery Hill they must first "ploy" from line into column of march before they start moving. This means organizing a large number of men, and if the reserve is a corps this can involve upwards of an hour's delay. Then they can start marching, and they have further to travel than from the "true reserve" position; this can multiply the response time by a factor of three or four.


Another example of where a reserve was handled in the "classical" way for a true reserve is the Imperial Guard, especially at Waterloo. As Napoleon committed the Guard, each battalion sent into action was drawn from what were literally men standing in blocks by Napoleon's headquarters. That's why they were called "The Immortals" - they were shielded from the day-to-day casualties of combat by the Emperor, who wanted his reserves fresh for the decisive moment. (They called themselves "the grognards", or grumblers, for the same reason - they weren't getting to fight.)

One can sort of think of reserves as the "quick reaction" force; if a crisis or an opportunity develops in an arbitrary point on the field, the reserves are the force that can be sent there the quickest. It's sometimes said that battles tend to be lost by the first man to commit his last reserve, and while this is too simplistic it does have a germ of truth - that being that once you no longer have a "quick reaction" force then when the next crisis develops you can't react to it as quickly as an enemy who does have a "quick reaction" force left; conversely if a crisis develops and you haven't commited all your reserves yet but your enemy has, you can seal off the problem.

If I recall correctly, general doctrine (throughout history) was that if you had all your troops committed and no reserve, then unless your line was under heavy stress and in danger of giving way everywhere then you should draw troops back out of the line to re-form a reserve. This is interesting because at Gettysburg on July 3 there is no true reserve left - the last corps to arrive has been parcelled out as penny packets in the "support" role, which makes the individual points of the line stronger but also means that if the line is breached there's nothing to use to react to it.

(Gettysburg is an interesting battle in terms of what it means for the management of reserves, and it shows Lee using Napoleonic operational concepts related to the idea of drawing out enemy reserves and only then committing.)
 
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The reason why a reserve is when a formation is uncommitted is basically related to distance and time. Taking as an example Gettysburg, which is a relatively compact battlefield, the fish-hook is perhaps three miles from north to south.

If the reserve is at (say) the modern visitor's centre and is uncommitted, this means that it's ideally formed up in column and ready to react. Once a message is sent to put them somewhere, the force can move out in relatively short order to any part of the line - given marching speeds over short distances, they can start arriving in perhaps half an hour or a bit more and begin deploying.
If however the reserve is on the left flank and is deployed as a second line, then if they're needed on the right flank or at Cemetery Hill they must first "ploy" from line into column of march before they start moving. This means organizing a large number of men, and if the reserve is a corps this can involve upwards of an hour's delay. Then they can start marching, and they have further to travel than from the "true reserve" position; this can multiply the response time by a factor of three or four.


Another example of where a reserve was handled in the "classical" way for a true reserve is the Imperial Guard, especially at Waterloo. As Napoleon committed the Guard, each battalion sent into action was drawn from what were literally men standing in blocks by Napoleon's headquarters. That's why they were called "The Immortals" - they were shielded from the day-to-day casualties of combat by the Emperor, who wanted his reserves fresh for the decisive moment. (They called themselves "the grognards", or grumblers, for the same reason - they weren't getting to fight.)

One can sort of think of reserves as the "quick reaction" force; if a crisis or an opportunity develops in an arbitrary point on the field, the reserves are the force that can be sent there the quickest. It's sometimes said that battles tend to be lost by the first man to commit his last reserve, and while this is too simplistic it does have a germ of truth - that being that once you no longer have a "quick reaction" force then when the next crisis develops you can't react to it as quickly as an enemy who does have a "quick reaction" force left; conversely if a crisis develops and you haven't commited all your reserves yet but your enemy has, you can seal off the problem.

If I recall correctly, general doctrine (throughout history) was that if you had all your troops committed and no reserve, then unless your line was under heavy stress and in danger of giving way everywhere then you should draw troops back out of the line to re-form a reserve. This is interesting because at Gettysburg on July 3 there is no true reserve left - the last corps to arrive has been parcelled out as penny packets in the "support" role, which makes the individual points of the line stronger but also means that if the line is breached there's nothing to use to react to it.

(Gettysburg is an interesting battle in terms of what it means for the management of reserves, and it shows Lee using Napoleonic operational concepts related to the idea of drawing out enemy reserves and only then committing.)
Great stuff, man. Thanks.
 
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Cody C. Engdahl, being in support basically means that they are in the fight and their intent is to assist and follow the lead of another company, regiment, brigade, corps etc... regarding a specific move, campaign, battle, fight or action. If they are held in reserve then they are held back in the rear to be sent where ever they are needed, if and when they are needed throughout the day or night. Typically when a regiment or brigade is held in reserve they are being rested after a heavy fight or after suffering heavy losses during a hard fight and are allowed to fall back to regroup and get some much needed rest, but remain on call should they be needed. Sometimes a regiment or brigade was held in reserve for strategic reasons to be used later to gain an advantage as reinforcements to turn a fight, charge the enemy`s works, meet an over whelming force, out flank the enemy at a key point of the battle or to relieve another regiment or brigade who have been fighting all day long and in need of rest.
 
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Saphroneth

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As a good illustration of when the usual story about reserves is wrong, we can look at Antietam.

It's often said that McClellan had 5th and 6th Corps in reserve at Antietam, or that he had ca. 20,000 troops in reserve. Neither is true, and the reason is twofold.

Firstly, because 6th Corps wasn't in reserve - it wasn't even in support. 6th Corps was the main battle line on the right flank and was shielding 1st, 2nd and 12th corps as they recovered from the shattering effect of the day's fighting.
Secondly, because the amount of 5th Corps that was in reserve rather than in support or on the front line was basically Morell's division, but Porter had come from the south of the Potomac and his reports of the south of the Potomac portion of the Washington defences was 20,000 - not that he was given that many men to take as reinforcements.

Interestingly at the time of the crisis on the Union left (AP Hill's arrival) McClellan's uncommitted reserve was nil. He'd actually committed his last two brigades from reserve to go to the Union right, but they were still marching when the flank of Cox's corps caved in and he recalled them to the reserve position.
 
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Saphroneth

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Something it's worth thinking about in the reserve context is what influence an army commander has over how the fighting is going.

In discussions with his commanders he can set them objectives, or tell them to watch out for something - things along those lines - but if he wants someone to attack the house on Winston Church Hill then that order has to filter down through CC and DC to brigade commanders. To have a conversation with CCs at an overall meeting after the march is one thing, but to change the course of the army mid-day is much trickier - and the corps commanders are busy fighting their corps.

On the other hand, since a reserve is uncommitted and not doing a job, he can send them on their way pretty sharpish. This means that one of the main tools an army commander has to manage a battle on the timescale of hours is to commit reserves, and in several cases (though not all) you can look at what an army commander's actually doing during a day of heavy fighting and it's that - whether by committing a centrally held reserve or by managing reinforcements coming onto the field and committing them (in the latter case units are effectively coming into reserve as they arrive on the field).

Wellington is a bit mad because he's effectively acting as all his own corps commanders, and in some cases division commanders as well - he orders many brigades into action personally - but Wellington was a superbly fit genius, and even then a lot of his management of Waterloo-the-battle (for example) is committing troops from his reserve while his other defensive masterstrokes tend to involve constructing second lines behind threatened first lines or ensuring a steady flow of reinforcements to threatened sectors.



It should also be noted that in addition to army-level reserves, many subordinate commanders would have small local reserves of their own under much the same principle. In WW2 the usual doctrine for a triangular formation was two-up one-back at every level, which means that a hypothetical infantry corps of three divisions of three brigades of three regiments of three battalions of three companies of three platoons would in fact be advancing on a front of only 64 platoons out of 729 - but it would also be very flexible, and if it ran into trouble on a company, battalion, regiment, brigade, division or corps frontage then reserves would be available.
 
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Cody C. Engdahl, being in support basically means that they are in the fight and their intent is to assist and follow the lead of another company, regiment, brigade, corps etc... regarding a specific move, campaign, battle, fight or action. If they are held in reserve then they are held back in the rear to be sent where ever they are needed, if and when they are needed throughout the day or night. Typically when a regiment or brigade is held in reserve they are being rested after a heavy fight or after suffering heavy losses during a hard fight and are allowed to fall back to regroup and get some much needed rest, but remain on call should they be needed. Sometimes a regiment or brigade was held in reserve for strategic reasons to be used later to gain an advantage as reinforcements to turn a fight, charge the enemy`s works, meet an over whelming force, out flank the enemy at a key point of the battle or to relieve another regiment or brigade who have been fighting all day long and in need of rest.
Thank you.
 
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