Land mines and other forms of buried explosives

You don't describe your superhumans as having any regenerative powers, nor super senses. So pressure-activated land mines are a great way to slow them down (if they're aware of their existence and act more cautiously) or cripple/kill them (if they trigger them). They're available with late 19th century technology, with pressure-operated mines using percussion caps having been deployed in the Crimean War (1853-1856). Mine the ambush site. Place it near many concealed escape routes. Drill your soldiers on mine-free paths to the escape routes. If the heavy artillery fails, and you're pursued, scatter through the mine field, hide, escape, regroup elsewhere. If the superhuman hits one while pursuing, well, your next shot will be a lot easier if they're missing a foot/leg, and might even kill them (early mines were sometimes just artillery shells with a pressure caps after all, and having one detonate in direct contact with their foot seems reasonably close to being hit by launched artillery). If one of your soldiers screws up and steps on a mine first (memorizing mine fields being rather hit or miss), well, the superhuman knows there are mines, but that just means they're less likely to pursue at all (you want to risk yourself chasing down a handful of nobodies at the risk of your limbs?).

Similarly, simply burying a large quantity of dynamite (invented in 1866) connecting it to a buried wire for instant detonation (modern-type electrically-triggered detonators invented in 1875), and luring the target superhuman to stand on top of it (they're not super-intelligent, you can find a way), while someone a few hundred yards away triggers the detonation instantly upon the target entering the area before they even know there's a threat.

Point is, trying to fight these people in active combat is playing to their strengths. Combat's not a sport, and you don't get points for playing fair. If the superhuman is aware of a threat, they can take steps to counter it, so don't ever let them see you coming.

You're actually looking down the barrel of one of the great issues with all the superhuman characters across the board. What does stop them killing everyone?

Achilles had his heel, Superman has his moral code, Spiderman and Batman depend on recurring enemy characters to keep them in business

In fact moral code is basically the only thing that stops them, of course that's until you get to the likes of Wolverine, but especially Deadpool, who on at least one occasion kills absolutely everybody including the authors of the comic.

So what's to stop them killing everyone? Probably short attention span. They get too quickly bored of chasing people for long.

Your basic tactic is to give the "every man for himself" call and scatter in as many directions as possible, some people will get caught but you'll only get the occasional combatant with the will and attention span to actually bother running them all down. You say you don't want them running around like headless chickens, but there will always be a predefined rendezvous point, the important thing is to not go there until you've lost your pursuer.

I see parallels with the Battle for Berlin in 1945 and the following allied occupation. The majority chose to live under occupation but a few chose to fight on for their cause. The occupiers did not have superpowers, but they had better weapons and could radio for air support, while you had to survive with what you could find. They used wire strung across roads at neck-height for someone driving in a jeep (jeeps later had a central pillar attached to the front bumper to frustrate this). They excelled in booby traps. An 'anti-officer' trap was a crooked painting which detonated a bomb when it was straightened. Potential 'war souvenirs' were made to explode. Light switches and door-knobs were electrified - this was not fatal but it did make people cautious, and that slowed them up. Their way to escape was always to turn back into a regular civilian once they had laid their trap.

Chemical warfare has been around since prehistory. Poison arrows, poisoned water, toxic smoke etc,.

Just shoot them with poison arrows or something. Powerful people surrounded themselves with body guards and checkpoints because anyone with a ranged weapon can kill them if they don't, and anyone who gets close enough can knife them. And they can't stay awake forever.

Why are ordinary human soldiers trying to ambush superhumans at all? There are a few reasons that I can see:

1. The superhuman is a threat to society, and needs to be captured or killed in order to protect society from them.

2. The superhuman is on the opposing side in a war.

3. Superhumans are somehow anathema to society, regardless of the actual threat that they pose, and must be captured or killed in order to satisfy whatever authority has declared them anathema.

Why do I bring this up at all? Because the motives of the superhumans that the soldiers are trying to neutralise affects the likely behaviour of the superhuman should an attempt to neutralise them fail.

In the event of 1, the superhuman being a threat to society, it must be considered, what kind of threat? If they're a super thief, con-man or other non-violent criminal, there's no particularly unusual problem. However, if they're a violent criminal, that's when a failed ambush becomes a serious problem. In the event of 2, the superhuman is a soldier, as are those who oppose him.

In the case of a non-violent criminal or most soldier supers, in the event that an ambush fails, the team could withdraw along a pre-planned exfiltration route which is prepared with traps such as lethal and non-lethal mines that can be activated after they have passed. The goal is to make it risky for the super to follow. Such a super may opportunistically or reflexively try to kill members of the team who ambushed them, but they're still people with a reluctance to kill their fellows, and they would have a sense of self-preservation. They would probably have other goals, and getting side-tracked to eliminate these ambushers would usually be an afterthought.

In the case of an anathema super, the tactical situation is even simpler. Most anathema supers will be interested primarily in escape to some more tolerant (or less familiar) region. A failed ambush should send them into flight and into hiding, so escaping their retaliation would usually be a minor concern.

However, it is the supers who are violent criminals or who have lost their humanity through long exposure to war or persecution who would pose the greatest threat. These supers may react with instant and indiscriminate violence to an attempted ambush. They may be unwilling to let any members of a team that ambushed them escape unpunished. They may be willing to inflict collateral damage upon large numbers of innocent bystanders in order to punish their ambushers.

In this latter case, such a super might be willing to hunt down and kill their ambushers to a man. They might take and eliminate hostages to convince their ambushers to surrender in order to minimise this collateral damage, or use hostages to trip traps left for them by the fleeing team. They might make a point that the damage that they're inflicting upon innocent bystanders is a direct result of the attempt to harm them.

When facing such a violent and ruthless super, failure to ambush them would require a rather different escape plan. The ambushing team would need to be wearing uniforms that they can shed easily, beneath which they would have civilian clothes. On the failure of an ambush, they would need to flee in as many directions as possible, get out of sight, shed their uniforms, and act like any other fleeing normal. It would be inadvisable to leave anti-super traps, since these could easily end up being triggered by other normals.

These teams would have to be able to act like non-combatant normals and simply flee, no matter the harm that the super they tried to ambush inflicts on either their fellow team members or bystanders. Failure to act like a hapless bystander would almost certainly lead to their mutilation or death at the hands of their would-be target. Even if they do everything right and escape, they would need to be prepared for the likelihood that innocent bystanders will be crippled or killed. However, the goal is for as many of the ambush team to escape and regroup so that they can try again later.

Ideally, an ambush against a known violent super would be conducted at long range using artillery or remotely-triggered explosives. If the ambush failed, that would put the ambushers out of sight and a long way off, and in the best position to disappear before their target can catch up with them. Less violent supers could be ambushed at closer range more safely.

The question seems to be "how do you run away from someone faster than you?" which is pretty hard. If you want to avoid sneak-attacks, that leaves attacking from somewhere the super can't reach (say a helicopter hovering higher than a tall building) or from an aircraft that is faster than the super.

Then you need some serious base-defence, like a CIWS. Modern weapons are super-powerful, missiles are able to hit supersonic targets and anti-tank warheads can punch through a couple of feet of steel. But they don't automatically overpower a super because they can't be carried around by every regular soldier, so you can still have a balanced world.

Because it's a war crime

And because it's petty.

The soldiers against them are mostly a non-threat. Of course, this is war, and there will be collateral damage, but this operate on the same mutual understanding that "Do not shoot at the medics".

The super-abled soldier will plow through towards their objective, until they meet an appropriate resistance. If a soldier is standing in their way being a nuisance, well, they are fair game - but most people know by now that they are only here to at most delay superpowered enemy soldiers, and to go to ground if they fail.

The super powered soldiers don't go out of their way to kill people for the fun of it cause:

1. (I quote) "they are not psychopaths or anything so they won't just kill people for the heck of it"
2. It would just be a plain waste of time.
3. If they start, the enemy will start doing the same, and now you end up with massive casualties on both sides.

(In a way, it's not too different from a tank - you may take a potshot at it out of duty, but if the turret swings your way, you duck and keep real quiet. On the other side, the tank does not pursue you if you are not a real threat, cause it would be pointless/petty.)

It's a sort of implicit agreement, or it has been ratified, and those who break that rule are hunted down and put down.

It's not to say it will never happen, it's to say it's rare enough that you can reasonnably track each instance and trial the responsible(s), and your hierarchy is enforcing that enough to dissuade most super soldiers to go off the reservation.

Ideally: Use a bomb

I am reminded of a scene from A Knight Tail

Adhemar: And how would you beat him?

Other Knight: With a stick. While he slept. But on a horse, with a lance? That man is unbeatable.

On the battlefield, your superhumans will be very costly to beat. So if normal humans want to kill one themselves, it is best to do it off the battlefield. Before your army even arrives in another country, if they have any superhumans, you will want to send special forces ahead to kill the superhuman before the fighting starts. Since your Superhumans are basically living tanks, you will need to use the same weapons asymmetric forces have always used to take out tanks: big explosives.

So the city where the super lives might be infiltrated by a few different teams, all with a different plan to rig a bomb to go off where he least expects it. One under his bed, another at his girlfriend's house, another under the table at his favorite tavern, etc. A few of your teams may be caught by town guards, but as long as one can succeed and catch the superhuman unaware, you can take him out before the fighting even begins.

If the Assassination Fails: Bait him into Cannon Fire

If you fail to catch the superhuman unaware, or if the enemy has a superhuman that you do not know about until it is too late, then you will have to choice but to face him in battle.

Even moving super fast, if he's in the middle of 100 of your guys, he needs to slow down a lot to kill them all. While his hands may remain moving at 200m/s, his feet might need to slow down to 20m/s as he hacks and slashes his way through your ranks... so instead of trying hit him with cannons while he is on the move, you need to aim your cannons at your own people. If you move a block of your men a bit ahead of the rest of your army, he will want to take them out first to prevent them from engaging and killing his own allies. So with cannons already pointed where you expect the carnage to happen, when he slows down to kill your troops, you fire a cannon barrage into the melee sacrificing your own men to hit him.

Dig a hole. Or a lot of holes.

In a few historic battles (and for the Viet Cong), digging small pit traps were a cheap, successful way to injure or slow opponents.

You can put spikes in them, but a hole is pretty good at screwing your opponent up.

And the same is true for a superhuman, particularly one moving at the speed of sound. If most of your body is moving at 330m/s, but your left knee and ankle are suddenly moving at 0m/s, well, for a normal person that leg is not staying on.

For a super, it's probably a different story, but still - that's a lot of energy, and it's got to go somewhere. It gets worse the faster the super is moving.

It's effective even if the supers know this to be part of the tactics - because they have to move at a slower pace, giving the ambushers more time to get out, or get another shot in.