Guide to Stealth

In this guide I will explain a bit about stealth.

Introduction

In a game like Aliens: Dark Descent, stealth can be very valuable even at normal difficulty settings.
And being detected alot will cause the game to get increasingly more difficult.

But keep in mind that stealth gameplay may not be to everyones liking.
My first advice is to consider starting a new campaign and adjusting alien hitpoints to lowest setting. The aliens still do the same damage, but they die much faster. On this setting, stealth can be ignored. Se my guide to Campaign Settings and Classes for more.
https://steamcommunity.com/sharedfiles/filedetails/?id=3204106078

I will in this guide try to explain my thought processes when considering stealth.
We will also look at how to improve your squad for stealth.

Stealth - Much to Consider

Is the alien coming this way? When will it arrive? Can I get away? Is there a place to hide?
Can I kill it without detection? Can I lure it away? Can I block its path?
How long can I be in line of sight undetected?

It's all about planning ahead.

Stealth - Detection Line

When there exists a direct line of sight between one of your marines and an enemy the detection timer starts counting down. This timer is visualized by a yellow line between the two. This line will start turning red from the enemy, and move towards your marine, until the whole yellow line has become red, indicating that the squad has now been detected.

If both are standing still it will have normal speed to get detected.
If eiher your marine or the enemy is moving, then it gets more complicated.
Running will cause you to be detected much faster than walking.
In most cases walking is best while in line of sight.

If the alien is moving towards you, then the detection speed is increased by the aliens movement speed towards you.
And if it is moving away from you, the detection speed is lowered by the aliens movement speed away from you. If the alien is moving fast, then it might lower the detection speed to it never detecting you before it is out of range.

This is useful when moving through corridors and you wonder if you can tail an alien undetected or not. Although, it is quite risky, should the alien turn and move towards you suddenly.

Here is a video from mission 1 with an example.
Notice how the detection line just gets longer at the end of the clip.
https://www.youtube.com/watch?v=yi5i7UANsEE&t=39s

Stealth - Half Cover

One way to break the line of sight is to duck behind cover.

Not every obstacle is possible to duck behind.
If you sweep the room with your mouse pointer/target, small green dots will appear behind obstacles that can be used to duck behind. Be aware it is important that the number of cover spots are more or equal to your squad size. Otherwise some might just stand there visible while the rest are hiding.

As long as the angle from the enemy towards your hiding marines do not get too sharp, you will remain undetected.

You can issue a move order to adjacent cover spots, to have your squad move while in cover. This is useful if an alien moves across the room you are hiding in. But if the alien is too close to your cover, it is a risk that one of your marines go visible for a tiny flash of time while repositioning.

Stealth - Full Cover

Some obstacles block line of sight. They also serve as nice places to hide behind.
But it can be tricky to know what is considered full cover and what is just obstacles which block your movement path.

When checking for cover, I use the grenade test. But I guess a sniper or an RPG also would do.
Just aim the grenade without shooting it. Sweep your target over the obstacle, and if it is full cover it will be blocked. Then you know if a line of sight is possible.

Here are some short videos from mission 1 focusing on how to detect full cover.
https://youtu.be/MQbuWYQOK5Q
https://youtu.be/uMCbom1kUm8
https://youtu.be/_S-ahXnqS84

Stealth - The Map

Exploring some rooms might get you caught in a dead end with an alien blocking the path out.
Take your time to study the map and plan your escape route and the time it will take.

Also, when detecting something on motion tracker, check the map to see if it poses any threat.
If you beforehand roughly know the layout, then you only need a second to evaluate the new movement.

Also be wary of alien spawn points if there are no movement nearby. An alien appearing while you are opening loot boxes is a serious danger of detection. If you are greedy, then have the recon with sniper rifle stand watch, and be ready for a speed duel when it spawns. Depending on alien hitpoints setting, a grenade or shotgun may also do the trick. RPG would take too long.

Stealth - Deployable Motion Tracker

Be sure to deploy motion trackers aorund the map. This will give you live positions on everything moving on the map.
This is excellent for studying enemy patrol routes.
It also gives you valuable input when choosing what path to take when crossing the map.

There is no limit to how many you can deploy, as long as you have command points,.

The most efficient strategy is to deploy some in a far corner of the map, where you already have explored, and then overload and destroy them one by one to have every enemy on the map gather there. This way you can explore without encountering anything. Be aware that aliens traveling to noise has a higher level of suspicion, and might have faster detection speed.

Stealth - Patrols

Every enemy has a set of different patrol routes.
If you watch on the map long enough you will discover every different route.

The difference in route sets are determined by what spawn point they originated from.
Therein lies a reason to leave some enemies alone if you notice they are doing the longer patrol route at the moment. Because if you kill it, it may soon spawn a new one that takes a smarter patrol route.

Also the number of patrols on the map is linked to the spawn points. There exists a maximum number of aliens spawned at the same time from each spawn point, normally one or two aliens. It is sometimes better to let them wander around if you plan to loot close to their spawn point so that you don't risk a fresh alien spawning while you loot.

Stealth - Movement Speed

Being stealthy is often a race against time. By just not being there when action arrives.
Getting out of the room before the alien comes in.

Take the perk Fast on every marine.
Each marine with Fast increases the whole squad movement by 3.5%. It stacks.
The recon class at level 6 gets Fast Deployment, 15.5% squad speed increase. It stacks with Fast but not with other Fast Deployment. Total squad speed increase over 30% faster.

Stealth - Flamethrower

As a rule, the aliens are afraid of fire.
By laying down flames across a door or hallway, it will cause aliens to turn around and go elsewhere.
As the flames lasts for 30 seconds it will buy you some time.

There are exceptions to this rule.
If there exists no other path, then the alien may walk slowly through the fire, in most cases this will kill it. Enemies that are not aliens will almost always walk trough the fire and die.

Stealth - Kill Undetected

One way to stay undetected is to kill the enemy.

In general as long as the alien dies from the first source of damage, it will not detect you.
Actually if the alien does not have line of sight at the time of impact, it also will not detect you. But an alien that has been damaged will have a very high state of alert. If such an alien should get line of sight on your marines, you will be instantly detected, there will be no detection line timer.
This is only true for what your marines directly shoot, does not affect deployables.

The best way to kill while undetected is the sniper rifle with the silencer upgrade.
It is safer to use the sniper rifle from behind half cover, because the marine will stay hidden while swapping weapons and turning, this would normally cost half a second of detection time in addition to the one second aim time.

The Overloaded Plasma Beam is also excellent at killing without noise. But its not without risk it seems. Shooting at sleeping aliens may get you detectet. Killing roaming aliens will not get you detected. Killing eggs will not get you detected. Killing human enemies will not alert them.

Killing undetected with the shotgun is possible, but requires you to shoot before the alien appears to already have the pellets in the air.

Deploying mines is a great way to prevent aliens to flank you or come down your dead end. If you can afford the command point cost. Enemies will not get a higher suspicion from the explosion, they just don't care.

The RPG is also a possible solution.
Its more difficult to aim, but a direct hit will do the job.
https://youtu.be/3zmtx4r5ikM?list=PL_NKLZwuyXz_1UAaZe4mayLkSCW4512jD

A well placed grenade from the Standard Pulse Rifle is also possible if it is a direct hit and alien hitpoints are not set too high.

And finally if you just shoot it with bullets, then in the very small chance you score a criticial hit with the first bullet, it dies and you stay undetected. That is called luck.

Stealth - Set a Trap

Sentry guns does not start a hunt or make you detected.

This creates the possibility to set up traps to kill off aliens.
Just deploy some sentry guns at the end of a hallway, and lure the aliens by creating some noise.

Here is a short video of such a trap on mission 1.
Notice the squad staying hidden and undetected.
https://youtu.be/ZCvn0OkWV-c

This is done to much greater effect if using a tecker drone to create noise and luring the aliens.
The drone can even lure facehuggers undetected.

Stealth - Cancel the Hunt

Sometimes a fight is unavoidable and detection must happen.
It is then very important not to let the hunt run out, but cancel it as soon as possible.
This prevents the aggressiveness to increase too much.

Besides jumping into a new scripted event, there exists two ways to cancel the hunt.

Taking an elevator.
https://youtu.be/IH5XjYCWomc
Welding shut a door to create a shelter.
https://youtu.be/aS82UfZ2u7I

Final Words

The more knowledge of the maps and patrol routes, the easier stealth gets.






Happy Gaming!

[Osselpi]

Excellent guide for me as a starting player. Foolish as I am, I started on nightmare difficulty and felt overwhelmed in the first mission pretty quick, although I had a pretty good run towards the first autosave point.

[Bazookamarx171]

The drone skill "make noise" from the Tecker can help you a lot during stealth bypass big groups as you can detach the dron from the squad and guide him making noise and drawing the xenos away from you.