During most wars of the 20th and 21st century replacements were sent forward to join units on supply trucks or helicopters. They were rarely sent forward as formed units as they were replacements for personnel lost in formed units along the FEBA. Now Combat units were sent to the Forward Edge of the Battle Area to enhance the combat units already deployed but that was usually when formations were in Movement to Contact and not yet engaged. It all actually depends on the tactical situation as to how personnel get deployed from a staging base.

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Generally speaking, attacking in marching columns is not a good idea. When attacking, you need to bring the right amount of force to bear against your enemy. A marching column is just a few men wide, a phalanx is dozens of men wide.

Commanders before powered transport usually have some set of scouts looking ahead telling them where the battle is so that they know where and when to get ready. As they get close they will deploy into a battle formation and engage in good order.

Battle is rarely the mass melee that you see in the movies so no, they don’t just show up and attack. Showing up and attacking without a formation or plan is a recipe for getting everyone killed.

Thanks a lot, that was the one detail I was missing, Scouts.

Great answer.... The reinforcement (although not strictly reinforcement) might be by opening a second front on the flank or rear of the enemy.

Re: Deployment of Reserves

About half a century ago the USAF sent a troublesome Col down to the basement of the Pentagon to keep him from causing more trouble. Was a bad move for the hierarchy as Col Boyd, having changed the criteria for the design of fighter jets, developed a presentation on winning and losing based on history. When the generals called for a 1 hour brief on the presentation Boyd stood his ground, it was an all day presentation that looked back as strategies over the ages.

Relevant to this discussion ------Starting around Page 39 it shows how "reserves" were used in many historic battles.

https://www.coljohnboyd.com/static/documents/2018-03__Boyd_John_R__edited_Hammond_Grant_T__A_Discourse_on_Winning_and_Losing.pdf

For those not familiar with the name , he drug the USAF away from large, complex fighters and is considered to be the godfather of the F-16. Rejected by the USAF top brass he found an intellectual home with the Marines where he fathered the Marine's land battle doctrine of maneuver warfare. Along the way he was the father of the OODA loop , originally created as a teaching tool for fighter pilots he was training.

An interesting tribute to Boyd appears in the Arlington National Cemetery site and is well worth reading . Pretty much the hero you never heard about . Observers noted that most of those in attendance were Marines . His teachings were the foundation of their success in the first Iraq war.

https://www.arlingtoncemetery.net/jrboyd.htm

During the American Civil War moving quickly from column to line was one of the essential skills recruits were taught, IIUC.

You can see some great examples in the movie Gettysburg, especially in the parts about day 1, when Heth's Confederate division arrives - they come in column and the officers direct each regiment into line, just out of range of the the Union troops.

>Or did their mere presence stop any thought of routing?

Let me tell you a secret about warfare: The average soldier has no idea what the hell is going on.

Even with all of our drones and radios, the average infantryman is really clueless about anything he can't personally see or hear. And in battle, 99% of your attention is focused on the enemy.

Now imagine you in the Napoleonic Wars. To your left, right, and rear are just close-packed soldiers wearing tall hats. You're already half deaf from gunfire and all of your attention is focused on the complicated process of loading your musket. If more guys are coming up from behind to help, you probably wouldn't notice.

It is not uncommon to see accounts of soldiers fleeing the battlefield, claiming all is lost, even when their side was actually winning. For example, at Waterloo British soldiers fled from battle and encountered Prussian reinforcements. Rather than being inspired to return to the fight, they told the Prussians the battle was already lost.

For what reason did you just post Fighter Mafia propaganda in this thread? You have one little link and a bunch of stuff puffing him up and lying about what he and his clique wanted the F-16 to be.

Were someone to read discourse on Wining and Losing they would not hear about jet fighters but rather about the strategies that resulted in winning and loosing over tens of centuries of wars and diagrams showing how reserves were used in various classic battles.

While Boyd would have preferred a simpler F-16 if fully focused on his strategy of great vision, highly maneuverable, affordable. His primary focus was on daytime fighter only missions. However , the evolution of the USAF mission called for all weather and some offensive air to ground capability beyond the gun. Boyd got 90% of what he wanted and the Air Force (and the air forces of many foreign nations) received what Boyd wanted and a great deal more capability.

Yes, thanks in large part to the Air Force bureaucracy Boyd left with few friends on the air side. But that served the nation well as Boyd inspired the Marine and allied land battle strategy for the first Gulf War that resulted in one of the most one sided battles in history. The Marines and a number of DOD officials gave Boyd credit as the foundation of their Maneuver Warfare strategy.