Why would large fortifications make a comeback in the near future?

Question

Why would large fortifications make a comeback in the near future? When I say fortifications I don't need Maginot line type defences, just fortifications in general. It could be closer to something like the Mannerheim line. Fortifications don't have to be prevalent everywhere. They only need to exist in some places as a defining feature of warfare. The technology level is near future. Most warfare is conventional between roughly equal powers. The 2 restrictions are:

1. No making people stupid, no disappearing tanks or airpower
2. No extreme environmental conditions, this is on a future earth rather than a different planet

Answer 1

Plasma Shields

Traditional fortifications went out of style because of a the linear-cube law. As world builders we should all know the square-cube law by now, but the linear-cube law is kind of the same but even more unforgiving. As the scale of a fortification increases at a cubic rate, its defensive capabilities go up at a linear rate. Imagine you have a wall, 1x2x10 meters, and you triple it up to 3x6x30 meters. you have increased is mass/size/cost 27 fold, but only tripled its ability to resist pentation.

Because of this relationship, in a contest between scaling up a weapon to pernitrate a fortification and scaling up a fortification to resist pentation, the weapon wins hands down... but what if you had a way of defending a large area that scales up at a linear cost? That's is where plasma shields come it. Unlike a wall, a plasma shield takes a source of energy and used an array of lasers to create a plasma barrier just in the path of an incoming weapon. Because its potential is not spread across your whole perimeter at any given moment, it means that if your shield array doubles in size, it takes twice as powerful of an attack to break through... or it can split its beams to focus on twice as many simultaneous attacks of equal power... or you could have all of your lasers target threats independently to wipe out a large swarm of cheap slow moving drones in the blink of an eye.

Current designs of plasma shields are powerful enough to stop High Energy Lasers, block explosive shockwaves, and maybe detonate missiles, but they are relatively small systems designed to go on a plane, but a much larger shield powered by nuclear reactors could potentially stop all sorts of weapons.

Now, the defender has a true advantage. To attack a fortress guarded by a shield you need to attack it with vehicles which are much more expensive than fortresses by size, and harder to make on a really big scale. So if you just make a shield array large enough, and attach it to big enough of a powerplant, it would become virtually unassailable unless you attack it with a force of truly extraordinary size. Even a nuke could be blocked by such a system if the lasers cause the detonation system to explode from the wrong point of origin before it reaches its designated distance.

... if shields are not in your setting, any other adequately advanced active defense system should work. Plasma shields just scale up best IMO because so much of the system is power generation which can be done internally on a particularly large fortification.

Answer 2

Drones.

Freaking drones. You can have the sweetest tank that cost your taxpayers millions, and some $30 drone comes and lands some high explosive on it. Or worse a cloud of freaking drones that cost less than cosmetic surgery intercepts your cruise missile, or your jet that cost the same as 20 of that tank that blew up earlier in the paragraph. And forget about people on foot. When it comes to war, drones own the earth.

Drones. They are too cheap and too fast and too destructive and there are too many of them. You gotta hide your precious self and your tech from those drones, and get them toe to toe with your antidrone drones. And that means you and your tech and especially your antidrone drones need to hide someplace safe where the drones can't find them and blow them up while you get your pants on and have your coffee.

And someplace safe means a fortress.

Answer 3

People devise fortresses because in the past, the cost of defense is cheaper than the cost of attack. The defender builds a very high and thick stone/brick wall (certainly not cheap, but the cost is spread out throughout time)and station X amount of people on top of it, and the attacker will need at least 5 times the amount of people and equipment (immediate and present cost) to take it (just look at how many people is scurrying up the ladder, and how many is being killed on the ladder by arrow, hot water, burning log in the movies).

It is not until recently, when the advancement in long range artillery technology and modern mass-production industry that reversed the situation. Even the toughest wall can't hold against the repeat bombardment of cheaper, and more powerful artillery rounds that can be sent off the factory floor around the clock.

Also, smart generals from all era and places in history always try to dismantle a fortress without turning it into a slug match. Sun Tsu has said that "Attack a forturess head on is the worst strategy", and Clauswitz (I forget whether it is him) has said something similar to "If you barricade yourself in an impenentrable fortress, your enemy will seek other ways to get to you." A fortress must have self-sufficient food, water, medical, and basic manufacture ability to resist a seige. Special forces has been used to sneak into the fortification to destroy these vital facilities. The larger the fortress, the more unfamiliar the inhabitants are to each other. This allows spys and sabotager to sneak in.

To make fortress prominent again, one of these factors must be eliminated. Perhaps this is after a nuclear war that decimated most of the factories around the world. The fortresses are the remaining factories, who needs to be defended with everything the defender has and who can pump out ammunition and other war machine as fast as possible while the attackers must use numerical advantage. Some new methods can be used to detect spys and sabotageurs, such as bio-integrated microchips or just a guard dog/bear/mechanical dragonfly.

Answer 4

fortresses are a massive expense to build, and are only options when those controlling military spending need a project to embezzle from. When the Maginot line was constructed it was already obsolete .. there was never a time when it made military sense. It was just that the generals approving their construction were a decade behind in their understanding of air power and repeating weapons. They thought, incorrectly, that tanks were all they had to worry about.

Answer 5

If you want just ordinary reinforced concrete bunkers, as you say, on Mannerheim line, then they are still in use, so you do not need anything new happening.

The problem is that superpowers and major powers have weapons to effectively break such forts, including missiles that can penetrate metres of reinforced concrete and tens of metres of ground. So don't expect the bunkers to hold powerful enemy for long.

On the other hand, bunkers have way more use in a regional conflict between small states, though they still can be defeated by recoilless guns and some AT launchers.