Working with a world with relatively high industrial technology, including good materials technology but no energy weapons or the like but modern-day ballistic technology.

Why not use the equivalent of pavise shields in combat, especially if the positions are fairly fixed? These would be fixed against the ground, rather than handheld in any way.

1) I imagine if made of appropriate materials, they'd stop most small arms fire. They essentially would be sandbags but directional.

2) Energy from bullets would just be transferred against the ground, so many considerations about dissipation with body armor would become moot.

3) It would have its weight considerations, but its a lot lighter than sandbags. Simple technology such as a car and wheels could get it setup.

4) It could be used a mount to help stabilize heavy weapons.

What would be arguments against them, besides the prominence of indirect fire? And if I wanted to go higher tech with them, couldn't they work with powered exoskeletons, becoming essentially a shield that is lowered from the back and put in the ground, kind of like Sundowner from Metal Gear: Revengeance (although that went thoroughly into Rule of Cool).

Modern-day small unit warfare (where personal shields would be relevant) is based on mobility and fire-and-move tactics where the goal is to outmaneuver an enemy force to deny it a defensible front. To that end it is in the warfighter's interest to stay light on his feet while carrying as much ammunition as possible. During an assault on an enemy position a small unit may have to advance and withdraw many times to in order to achieve a tactical advantage. While defending a position from an enemy assault the unit may quickly followup with its own counter-assault. Given that the modern warfighter is already humped up with as much gear as he can physically carry and be effective in that environment it seems unlikely that the additional burden of a heavy personal shield would be welcome or net effective since other gear, likely ammo, would have to be sacrificed to make room for it. (Although infantry robotics, which are no longer the realm of sci-fi, may soon change that.)

Personal shields would also have questionable effectiveness against the more serious threats to warfighters such as RPGs and grenades, machine guns .30 cal and above, mines and IEDs, or even small arms fire effectively delivered (e.g. ambush). The extent that an injured warfighter would be willing or able to carry a shield is also questionable.

Modern warfighters are trained to use terrain and structures for cover and concealment, and against other infantry that is very effective. The stalemates of WW1 proved that. A shield on the other hand would provide relatively limited cover and no concealment on the battlefield. I suspect that is the fundamental reason why history has rejected the pavise for modern warfare.

Things like that have been used in niche applications.

• You mentioned ballistic shields. Before they were portable, they had wheels.




• With a little gun, they would be something like Gruson's pillbox.




• Crew-served weapons would come with shields, like this MG08.

My conclusion from these examples is that pavise-style shields work only in very special conditions, and that general issue would be either lighter body armor or heavier vehicle-mounted armor, not this "too heavy to carry, to light to protect" intermediate size.

Autonomous drone shield bearers.

Samuel 17

4 And there went out a champion out of the camp of the Philistines,
named Goliath, of Gath, whose height was six cubits and a span.

5 And he had an helmet of brass upon his head, and he was armed with a
coat of mail; and the weight of the coat was five thousand shekels of
brass.

6 And he had greaves of brass upon his legs, and a target of brass
between his shoulders.

7 And the staff of his spear was like a weaver's beam; and his spear's
head weighed six hundred shekels of iron: and one bearing a shield
went before him.

If you are in a fight it is nice to have a shield. Even nicer to have someone carrying it for you. In your future (as now!), the public is wary about having AIs with lethal force. Offense is reserved for humans. Defense however is another matter.

The drone shield AIs are in constant communication with each other but also make decisions independently: flocking behavior. They realign and redeploy according to the movements of those they are designated to protect, and their own perception of offensive threats. These would be fun to write, because the drone shield AIs will surprise you.

Ballistic shields are used in many police applications, as well as less armoured shields for riot and crowd control (where the threat is not considered to be firearms). This company offers a wide range of ballistic protection, including hand held shields, mobile shields and even "kits" to build defensive bunkers.

However, these sorts of devices are heavy, bulky and impede the mobility of soldiers. As a matter of fact, they don't even solve the greatest issue facing soldiers, which is overhead protection. What soldiers might really like in a defensive position would be something like a table with short, collapsible legs capable of protecting them from a shell burst overhead. Placed over the top of a fighting position (shell scrape, individual trench or fighting position), this sort of overhead protection would be appreciated.

Except that to be able to protect the soldiers from the blast and splinter effect of an airburst they would be carrying around something with the equivalent protection of at least 18" of earth. Considering that Russian weapons have grown in mass and firepower, the protection provided by 18" of Earth, while possibly sufficient for 122 mm howitzer or "Grad P" multiple rocket launchers, now has to contend with the equivalent of 152 mm "smart" rounds or even 300 mm multiple rocket launchers delivering their ordinance in a matter of seconds.

BM-30 Multiple Rocket Launcher

So these things would be massive and a huge pain to carry, plus they would need to be properly "bedded" into the ground, which can be tricky depending on what sort of ground you are on. This would be an engineer task, while the ordinary soldiers would be using corrugated metal, wooden beams or logs and other improvised materials to build their own overhead protection.

Laying down a supporting structure

*Cross section from a military manual

What the end result might look like, assuming that is an entryway under the three layers of logs

Since your engineering troops and transport resources are always in high demand, training the troops to make their own expedient cover out of local materials seems to be a much better use of resources.

Tanks

Would your shields be heavier than tank armor? Because we have weapons that can defeat quite thick metal armor. The history of warfare is a competition between offense and defense. If, for some reason, sitting still where indirect fires can target you all day were a tenable strategy, then attackers would simply switch to higher-velocity rounds. Why does this work? Physics.

Armor

Normally, we think of ballistics in Newtonian terms, and consider the momentum of the projectile vs. the hardness/tensile strength/energy distribution properties of the armor. For small projectiles moving at a low Mach number, this framework is adequate. The essential point is that we are thinking about a solid vs. solid collision, and modelling the result.

Armor penetrators come in two varieties: chemical or kinetic. They both work on the same principle: switch from solids to liquids, which can be easily penetrated and have close to 0 tensile strength (resistance to bending/puncturing). In particular, you want the target to become liquid. No, this does not mean using a flamethrower or comic-book magic, but yes, it does mean creating a jet of hot metal. The chemical variety creates the jet at the point of penetration (c.f. HEAT rounds), while the kinetic variety provides the penetrating velocity right from the launch point (c.f. APFSDS shells).

Deployment

Since these are expensive weapons, you would generally not arm all infantry soldiers with them. However, if this was the only way to overcome enemy defenses, then you can rest assured that every army which could afford it would field such weapons as densely as necessary (say, one for every fire team or squad).

Countermeasures

This is why modern battle tanks use active armor: the only effective defense against such weapons is to trigger them before they actually come into contact with your armor, and try to deflect the jet. Obviously, by this point we are talking about something quite a bit more sophisticated than a glorified sandbag.