Basic Training - The Ambush

"All warfare is based on deception." - Sun Tzu

The ambush is the basic component of warfare for any infantry (or indeed every hunter, fisherman, or trapper) worthy of the name.
Master it, and live. Fail, and die.

ambush n.: a surprise attack by people lying in wait in a concealed position.

It combines most of the tactical principles of war into one simple lesson:

Objective
Offensive
Mass
Economy of force
Maneuver
Unity of command
Security
Surprise
Simplicity

A hunter in a deer stand or a duck blind is an ambush. Every trapper's trap ever placed, and every fish hook hiding in a worm is an ambush. As is every submerged submarine torpedo attack in history. So is a mugger in an alley.

And still, it's easy to get it wrong, if you're an amateur and you don't know what you're doing.

Conducting an ambush assumes several things:

There's someone you need to ambush.
You can identify them positively when you see them.
Your team leader can therefore control whether or not to fire by the members of the team if #1 and #2 are not the case.

I've lost friends in the real world to slob hunters who shot at unidentified movement in the brush; it's even less funny when we're talking about slob infantry. The common words for that is brigands and bandits, and they usually end up shot themselves, or swinging on a rope, neck-first. They are everyone's common enemy, which is a lot of opposition to bite off and chew for your little group, especially if you don't have to do so. Don't be those guys.
Learn the difference between enemies, and unknowns, and how to deal with each one.

So, assuming you can tell who's who, what next?

Determine the type/style of ambush. The classic forms are Linear, L-shaped, and Area/Dispersed.

Linear ambush

L-shaped

Area/Dispersed Ambush

Other ambush type variations

But the varieties are really limited only by imagination, provided you organize them properly.

1. Select the site.
Pick terrain favorable to you, and unfavorable to your intended target(s).
In A-stan, the mujahideen work with light arms, from mountains. Their kill zones are roads below. It works great, especially against road-bound enemies heavily-burdened and tied to vehicles. Ask the Soviet Army about that. (Against supporting arms like artillery and air, with no such mobility problems, and no means to counter it, not so much. Which was why we gave them Stinger MANPADS missiles. The Soviets got their clocks cleaned, and we did commensurately much better, because they didn't have missiles to shoot down our air cover.) Takeaway lesson, the terrain must be selected to take advantages away from your prey, and hand it to you.

Nota bene: The enemy gets a vote. They know about ambushes too, unless you're unnaturally lucky, and meet someone who's clueless, in a Darwin Award-winning manner.

So barring that stroke of fate, they'll naturally be warier and on higher alert when entering ambush terrain. You may have to use elaborate and problematic means to draw them into apparently open terrain in order to spring your surprise, as in the first vignette in this clip:

2. Secure the ambush site.
Nothing would be worse for you, than to be ambushed in your ambush site, while planning and setting yours up. You have to reconnoiter and clear the area, and do so without making your presence obvious, and keep it so until your trap is ready.

Your security element also serves as the gatekeepers on the ambush site, keeping watch for any target(s) approaching the trap.
They also need to know an ambush-worthy target, versus one you might want to let pass by. Think in terms of size. A patrol team or squad shouldn't bite off an ambush with a battalion of several hundred guys as a rule, unless they all have terminal cancer and nothing to lose.
But a lone platoon wandering around fat, dumb, and happy is another story altogether for that same squad. IOW, leveraging surprise and initiative into 3-to-1 casualties is reasonable, and perhaps necessary. Expecting to inflict 20-to-1 or 50-to-1 casualties is farcically foolhardy and futile.

3. Set up forces to conduct the ambush

The team leader on an ambush patrol, whether the ambush is hasty or deliberate, needs to individually place every person where he can see them, communicate with them, and control them, and they must be "in the loop" non-stop, with every person acting in concert, or else you risk premature inititiation, which could turn failed surprise into your funeral.
It is exactly like a symphony: the entire band has to be on the same sheet of music, and the conductor sets the timing.

Know also that your ambush may be conducted relatively near (i.e less that 100m away) or far (greater than 100m away). Those distances are arbitrary, but should give you an idea, for planning purposes. Near ambushes can expect a trained enemy to charge your forces. Plan appropriate disincentives to this response. Spikes, barbed wire, etc.
In far ambushes, the enemy may elect to remain in place, find nearby cover, and attempt to return effective fire. You may wish to do things to make taking cover nearby problematic for them as well. Nasty surprises in nearby ditches and behind boulders, etc., are long-standing procedure in ambushes, as Blaster will explain:

In planning, be aware that enemy columns put out security to the front and flanks, since forever. It's rather awkward to have their flank security wander right into your position, as they're designed to do, and then be yourself surrounded by the larger force now alert to your presence, and pummelled into hamburger by them, because you were inside the boundary of their flank security. Pay heed to that lesson.

4. Assign key tasks and targets
Someone may be designated to hit high-priority targets. These would include, in order, opposing command and control, radio carriers, and anyone operating crew-served weapons like machine guns, especially if your team lacks them. A machinegun against 10-15 men, even in cover and concealment, isn't a disparity of force, it's a turkey shoot. You're the turkeys on that cast list. If there's no command and control, no means of calling in supporting arms, and no force multipliers like automatic weapons or grenade launchers, it's down to your guys under cover vs. their guys, in the open. Shoot priority targets first, every time. Life is dear, and bullets are cheap; use more than one.

5. Set up signals plan
You'll need a way to convey signals for shoot/no-shoot, initiation of ambush, and breaking contact, and actions afterwards. If it's an annihilation ambush, where you destroy the opposing force, you'll need a signal to enter the kill zone, and gather any material or intelligence items. You may even elect to bury the bodies, making discovery less likely, and preventing whatever larger force may have sent the targets into your area from knowing what happened to them.
Or, if things go wrong, the force isn't subdued/destroyed, or their QRF forces reinforce them before you break contact, you need to be able to tell everyone when to cheezit, and get outta Dodge, without it turning into a rout.
You'll need primary, alternate, contingency, and emergency signals for all the above situations.
Ideally, these should all be group-standardized, and part of your patrol SOP, so you only have to do a cursory reinforcement each time out, rather than re-inventing them wholesale, on the fly, time after time.

6. Actions afterwards
Prisoner details, search details, weapons recovery, material destruction, and who'll carry off what, for openers. Burial details possibly, as well. You'll also need medical and casualty evac people assigned; rounds going both ways make you getting off scot-free unlikely.

7. Establish after-action rally points
Everyone should know your primary and alternate places towards which to exfiltrate and fade away, in case enemy action or other eventualities require your team to split up and reconsolidate elsewhere afterwards. Everyone needs to know where, and for how long, each one is active.

8. Wait for a target

9. Initiate the ambush on command
This is the leader's job, based on the information from flank security.
The signal to open fire, if desired, must be foolproof, and immediately understood.
This is why signals that rely on a chain of intitiation, like explosives, need back-up. Things go wrong, and getting a fizzle or a click, when you wanted a bang, is never a good idea. Have redundant redundancies. E.g. "When I shoot, everyone opens fire. If my round misfires, I'll blow this whistle." are better than "When Enemy Squaddie X steps on this cleverly-placed boobytrap, we all start shooting." Squaddie X may not have read your script, and no one steps on the initiating device. This lesson has been written in blood. Don't add a new chapter.

10. Take care of business - rapidly.
Like a bank robbery, every minute you're ambushing someone, is another minute reinforcements may be setting up to ambush you. Do unto others, and get it over with ASAP.

11. Cease fire and enter the kill zone, or break contact and head to rally points.
Command and signals for each option.

Then either depart, or enter the target area, search and strip what's useful, or destroy it. Then split. Orderly, but in haste, once you've accomplished your objectives. Security watching outboard as well as towards the ambush is critical at this point. Police up all brass and anything else to minimize information and intel to enemy follow-up forces sent to look for the missing group. Even if you just haul it a distance away and bury it, make everything you can disappear.
Account for all your people, signal security to collapse back, and un@$$ the area.
The less trace you leave, the better. It confuses and demoralizes opposition to fight ghosts.
If, at some point you choose to leave things behind to point to another entity as being responsible, even a mythical one, this is the time to do that.

12. Patrol back to your next objective, or return to base with your casualties, prisoners, and spoils.

Although the typical examples posit the ambush in a rural setting, be well aware: there is nothing whatsoever that prevents everything in this lesson from being applied in an urban or suburban environment. Precisely as rival narco-cartel gangs, and occasionally government authorities in Mexico and other failed states find out on a regular basis, week after week.
Vehicles block targets in a kill zone, and the assault element opens fire. Done correctly, it's brutal and overwhelming. Something even Hollywood (with Tom Clancy's help) could get right.

The only way to learn this, as "fieldcraft" ought to make obvious, is by learning it and practicing the details in the field. By all means, practice it on paper, or even rehearse it as a group on a tabletop with Little Green Army Men (if it sounds stupid, but it works, it's not stupid! No points for guessing how many {that would be all of them} multimillion dollar stunt and driving scenes in movies you've watched are rehearsed by the stunt men with a lunchpail full of little green army men, and Matchbox and Hot Wheels cars. Gospel serious.). But nothing is as good as actual training, out in the boondocks. This is why all military bases are sited in BFEgypt, by design. A number of the entities in the upper right column offer regular skills training out in the woods, and will likely put you in the position of ambusher and ambushee, to drive the points home. You are strongly and heartily advised to take advantage of those training opportunities, or similar, before you get a pop quiz on this information whilst out and about.

You can be the ambush master, or you can be its prey.
Your choice.

{ BTW, read the comments on this post.-A. }