eli5 how frontlines in war work


I have always wondered how frontlines work. Aren’t there always holes in the lines that the enemy just can walk through? Or are there really soldiers on every mile of the line?

I might sound dumb asking this but really, how?

In: 4

While there are gaps people could in theory walk through, guns can shoot projectiles over long distances so if someone tries to go through the gap, they are left as somewhat less of a man than they were before

It depends.

There are wars with front lines, such as WW2.

There are wars without front lines, such as Afghanistan.

WW2 involved millions upon millions upon millions of soldiers. This means that pretty much all of the front could be manned. Were there holes? Yes. What happened when there were holes? Either the enemy broke through it or you moved back to somewhere where you could shorten the frontline so you could man it.

Generally speaking a division was only seen to be able to man a couple of km of the front. In reality though a division could be stretched over quite a distance if need be.

And an enemy breaking through the frontline has to be able to maintain a line of communication and supply. It’s all well and good if they break through but if the enemy then cuts them off by closing the gap then that can be trouble.

Gaps would also be places where things like minefields would be laid. This way it’d be slow to cross them and the defenders could then reposition if needed.

The reason it was different in wars like Afghanistan was that the enemy wasn’t a state. They were insurgents, terrorists, whatever you want to call them. They might have controlled some territory but quite often they were just people who popped up from place to place. This meant that a frontline wasn’t something that would normally exist, except maybe in a few places where they decided to stand their ground and fight, such as for a city or their mountain bases. Otherwise it was US and allied troops ferrying around in things like helicopters and going wherever the Taliban, AQ, etc just happened to be that day.

The simple answer is it depends.

If you look at WWI there was a continuous trench system from the Swiss border to the Atlantic coast. This is the exception.


Most of the time you are limited by the number of troops you have and the concentration you need to be an effective fighting force. There is usually also a limitation on where the enemy can go with rivers, forest mountains, etc so most troops will be where it is possible to move around. You need support with vehicles today, wagons in the past for something like armies we know today so there is terrain limitation.


It is reasonable to have enough soldiers out there so all of the front it observers. But you can cover larger areas from a single location. You do not need them at the border, it might be a good idea to move back a bit from it to a location that is simple to defend or a better observation position.

In war, a “front line” is generally defined as a set of points at which two opposing forces are engaging each other. It can refer to an area as tiny as a few hundred meters where two infantry units are battling or an area as large as an entire continent when massive armies are involved. When you’re talking about very large conflicts, of course it’s ridiculous to think that there would not be any gaps. Even though we have weaponry, such as missiles, that can feasibly strike *any* point on planet Earth (and subsequently would be able to strike any point on the front line of a theater of war), it is unlikely that any fighting force would be monitoring *every single point* simultaneously in order to respond to a cell moving beyond what is otherwise identified as the front.

Some military conflicts don’t even have a front in this sense. Fronts generally occur when two opposing forces occupy different geographical regions and are trying to capture each others troops, equipment, leaders, capitals, or other strategically important assets. But when two opposing forces already occupy the same contested region, a front ceases to exist because both forces are constantly surrounded by each other. This was the case between NATO forces and the Taliban, for example. *However*, because the definition of a front is rather fluid, it would not have been unreasonable to say that literally any skirmish or battle temporarily created a localized front.