This guide is primarily created to show you tactics that my crew and I come up with to successfully stealth whole Join or Die mission on overkill difficulty.
This tactics used to be able search all loot crates spots unrestricted and keep the noise level down to zero up until escape.

This tactics requires some strict requirement for level, guns, power level and order following. If you don't have all needs to fulfill this requirements you always can play around. This tactics don't guaranty 100% success chance since sometimes things can go wrong. But following this guide will give you pretty much high chances to things go as smoothly as they can.

!UPDATE!

Since new patch rolled in, section about key in second camp is no longer 100% valuable and yet (probably never) updated. Take old tactcis with cautions. You still can possible use the pattern to just clear the whole second camp and find key later. Good luck.

Let's get started.

If you want to make this mission solo, you need to play as Grant. Not much to say about it. You mark for death is what makes you an unstoppable killing machine, master of stealth, horde crusher, one man army. Make sure your Grant have maxed Marked for Death damage increase (+40% dmg in total).
If you using sniper rifle, make sure you skilled your Sniper rifle Proficiency (+20% dmg).
This also can be done with other high dmg weapons such as shotgun/crosbows.
Basically, you want to able to kill enemy under Mark for Death with single shot.
Your handy tools will be Wire Cutters to be able to pass inside the camp undetected.
For team composition, you can have anybody on your team as long as you have Grant, but even if you don't have high level Grant with you, you still can try to follow this Pattern of Killing to maximize your stealth abilities.
More than 2 Grant character in team is OVERKILL. One Grant can do the job, Two Grants can do everything on a light speed.
This patterns, of course, is easier to follow if you have high end gear, but we started using this tactics when our Grants can't kill enemy with single shot and have to work in pairs to save silencers and make follow up shots on a single target.
One other little thing you want to have is level 3 Range station.
This will boost your performance and allow you to run around and not being noticed by nearby enemies and simply walk to your targets rather than slowly crouching.

Alright, you made it for your first human encounter. Here is simple overlook what we are dealing here with.
7 targets. One of them on patrol, heavy armored guy (Shield). Sniper will start outside and make his way inside the Cabin and stay there.

Make your way past Boxes and Debris, making sure you not going to alert troopers near HMMWV at the yard. Your first stop is near Control Room.
Two guys (Shotgunner and Trooper) is your first targets to kill. Before you engage, make sure that Shield is far away or making his way to the yard.
Here is how you can kill them.
1) If you high level enough and wielding Quarterstaff you can just give them good old One-Two. Mark them and Charge strong attack and just SMASH this boys to death. It will take one full strong attack combo to deal with them.
2) If you playing in team, just have a buddy to make double takedown. This is text book stuff.

After couple being done with, run past army truck to 2 Part Container and wait till Shield make his way back to Control room. When he spot dead bodies, he going to stuck there. Yellow sign will be your green light to start your chain reaction pattern killing.
Tree Troopers are now your targets. Mark them as they go or pre-Mark them before engaging.
Take down a guy near Cabin and wait till his buddy will check on him.
After second Trooper is down, take a peek and kill last guy near HMMWV.
Just two guys left. Walk out Container and stealth takedown Shield.
Only Sniper left. Kill him as you like. Walk to him and make a takedown or just give him good old One-Two.


Walkthrough video.
https://youtu.be/-qt_WyV1kBk

Here are quick notes about this part. You can use any means to kill snipers on walls. This will not alert guards inside, if you being spotted. Don't forget to check every crate spot. But here is a thing I noticed. When you checking far left side for crate in bushed, make sure not to alert any walkers near gates. This may trigger guards inside to start attacking them and messing any means for your future stealthing inside the camp. You may kill sniper from far left position if you will, but it will not make any impact for inside part.
So just make rout near map boundaries to check for case and get back to drain pipe, secured by wire and get in. I hope you saved one wire cutter for this, right?

So here we are. Brigade camp. This is the hardest part and have many variables to deal with. But it's not as complex, as you may think. Here is a simple overlook what we are dealing with here.
Whopping 13 enemies are presented in this area. We going to split this into 3 small areas. Devine this into small easy achievable goals. I read this from management books. Lester from GTA5 told me this.
1. Entry point. 3 Troopers and 2 snipers. We going to make some room to breathe.
2. Tented Area. 3 Troopers and 1 Shotgunner. At this point, we almost finished.
3. Shooting range. 2 Troopers and 1 Shotgunner. After this, we are in the clear.
Here is the funny part. Shotgunner, who carry the keys, are not going to be presented in any specific zones, because he has a long patrol rout. Be aware of his presents and try to take him away at Entry point area or behind containers where no enemies are presented.
But, if you have two Grant characters in your team, you can split Entry point and Tented area and meet around Shooting range. But if you playing solo, I encourage you to do this in this order. This is what this guide is all about. Patterning your movement. You can start this from second Entry point, but you need to find keys for this. But at this current moment keys are not spawning and forcing you to take longer route. But I actually like this route since I can check all loot crates and have clear and it's harder to deal with Entry point 1 if you start from Entry point 2.


First things first. When you get up from pipe, mark two Troopers in front of you and make a double kill. Just line them up and shoot them up. If you cannot kill enemies with one shot... well, use your imagination on this part. :) I bet you can just stealth takedown them both.
Take turn to the right and get up into stacked containers. You will have a good spot to kill two Snipers.
Don't forget about one guy behind the Military truck. Take a peek and take him away. At this point you can encounter Shotgunner with keys. If he spot any dead bodies in this area, just let him get close, so Troopers at the range doesn't spot him.

Tented Area.

Now make way to Sniper Tower near second Entry point and follow road near cabins. You will need this spot at first screenshot. You want to take down Trooper inside Cabin. He will appear from Cabin for a very short amount of time. You can mark and shoot him as he get outside, but for your first try I suggest to mark him, wait till he get in and get out and make a shot. We want him to fall down behind sandbags and not disturb couple of Troopers near HMMWV.
Now, make your way back behind Tented Area. Mark all 3 enemies through container and get ready for chain reaction killing pattern. First, guy behind the Box. Make sure to make body shots.
After first shot, nearest enemy will run to check on his buddy. Sometimes Trooper will go and check on guy inside the Cabin. But it doesn't matter if he stay or go. You will have enough time to get him.


I hope you doing good so far and everything is going smooth. Now only last 3 guys left. Here you can go creative. You can stealth takedown patrolling guard (yes, he is close, but you can do this).
And finish last two guys as you like. Mark them, stealth takedown them, give them good old One Two or just shoot them. They are only 3 guys and they not going to make so much trouble.


Walkthrough video.
Quick note: Because I didn't kill sniper from outside, Trooper behind Military Truck starts moving behind containers. It's actually not bad and saves you a bullet.
https://youtu.be/WgH9jdeeuyw

After clearing Second Camp and opening the gates, go through military tents. We have only 3 enemies here so we don't need overview. But there will a major tip for next part.
Take down a guy in door way.
If you were quick enough proceed and just take down sniper as you please.
Follow the road and on the right tent you will find last guy. Stealth takedown him and loot around.
Alright. You may or may not aware that enemies spawn after you pass certain point on map. In this case, after you pass this line after HMWWV enemies in next camp will spawn and you don't want to spend whole lot of time around here. Loot HMWWV, loot cabin near gate, jump down, check loot crates spots and get behind the gate for our next camp.

Walkthrough video.
https://youtu.be/qbNeNLYwviM

This is it. Last very important camp to do in stealth to be able to clear mission at ease. Our main goal is not to get even one level of horde so Hurst will be outside the vault. After you enter codes for the gate, you can go all loud, but I encourage you to stay stealthy up until the escape.
Here is what we are dealing here.
9 targets to deal with. From the outside looks like a bit complex task but I have created very smooth path to deal with them. Mostly stealth takedown used. Let's get started.
Remember when I told you about spawning point before this camp? Well, if you didn't waste to much time getting to the entry point, you should and must take out Trooper who is making his way to Radio Truck. Simply walk up to him and take him down. You still can take him unnoticed if he didn't pass Cabin all around.
Now head your way to 2 floor building with kitchen inside. Don't be afraid of this Trooper on stairs. Simply make your way along the stairs handle and he will not spot you. But don't waste too much time around, because Sniper in 3 floor building will take time, but eventually make outside.
Just make your way inside. You will find mid-night Sniper who looks like he is hungry. Make him hungry for your cold steel, make sure not to alert 2 enemies inside.
Next we will need to deal with two chatting fellas inside the room. Mark them and be creative. If you have strong sidearm with silencer, just shoot them. Or quick scope them, if you have the skill. Or simply throw your Molotov in Shotgunner and finish them rightly (takedowns or with simple One-Two).
All this hustle not going to alert anybody in the camp as long as you don't give them time to react.
Pass this room and make your way outside. Take a ladder upstairs. We almost done here. At this point, depending how fast you are, Sniper could still be inside or take his way outside.
From this point you can deal with Trooper outside and Shotgunner inside. Shotgunner is taking long patrol route through Barracks so you can pick him at any point you spot him inside. But before you do that, closest Trooper will try to spot you upstairs. If Shotgunner nowhere in sight, just kill Trooper first. But be quick, because you are actually very close and very easy to be spotted.
Go through the building. If you quick enough, Sniper will still be inside. If not, he probably will stay outside and be confused by dead Trooper outside. You actually don't really need to mark him to give him good old One-Two to deal with. Because he is the weakest human enemy in game. But mark him for sweet extra dmg anyway.
The last guy who still standing is located just under your feet. He is guarding PC room downstairs. Deal with him however you like. Sometimes he could be disturbed by Sniper scream upstairs and make his way to check things out elsewhere. At this point, he is just one enemy and can be dealt with anyhow.


Walkthrough video.
Quick note: Because I didn't finish off sniper and let him raise the alert, last Trooper was alerted, but he actually was in right place to be dealt with.
https://youtu.be/2weCCyzdP-s

You almost done with perfect stealthing, but you not done yet. And here is the point where I see so many players make a simple mistake to take fight with incoming back up as they do code puzzle.
The trigger for the Hurst being outside and not inside his vault, is when you push PC to unlock the gate. If you get one horde level before you activate the codes for the gate all this hard work is for nothing.
So here is my simple trick to do this right. It's simple as it can be if you playing in team, but it's also simple and fast to do solo.
Activate PC, write down codes in chat as you like. You only need 4 digits to tell if the code is right, no need to write whole code. Mostly people will choose from first 4 digits and last 4 digits. I like last :)
Before you start, I recommend to find right codes to all 3 PC. First and last line is used for 3d floor building, representing top and bottom PC. Middle line is used to PC near your starting position at 2d floor building.
As soon as any PC codes will be entered, Brigade back up will come from gates near Sniper tower and Cabin near Entry point. You want to avoid them at any means.
Note: Here is the reason why you don't want to pick up a fight with them before you finish with the puzzle. Each successful code entry will trigger additional Brigade soldiers to spawn, if you in fight with them. In worst case scenario, you enter the code, fight first wave and do this two additional times for each code. Why waste bullets and suppressors when you can just lay low before you done with the codes? When you solve the puzzle, there will be no additional back up for the first Brigade group.

So here is what you want to do.
1) Activate bottom PC.
2) Run upstairs, activate top PC.
3) Run through the room and jump down along the gates and make your way back to last PC.
4) Activate last PC and enter the code.
Here is the path on screenshot.
When you see green light, you just successfully made Hurst to stay outside the vault.
Deal with enemies outside. I suggest to let them get closer and start from someone who stay behind so you don't alert whole party. If you have team at your disposal, just mark them for your team to deal them. Remember, good Grant is marking as much as he can, because your team will need same one-two shot to kill and don't waste their ammo and suppressors.
Quick note: If somehow things go ultra loud and Hurst run away from the Memorial, don't kill him. It will teleport you behind the gate and could possibly cut your loot away. And this is also put you on the spot where a lot of enemies presented and more will come later. So keep this in mind.
Carry any weapons your collected so far through gates and make your way closer to the Memorial. Here is what you've been waiting for. Hurst is here and he is an easy mark. There is only 4 enemies in total. Mark them all and kill them all. Important note. After you kill Hurst, it will trigger small back up to run to Memorial, already in combat state. If I recall, it will be 4 or 6 enemies total.
Don't shoot your flare just yet. If you didn't find all weapons/mods loot crates, check area around and collect ammunition for final standoff. As soon as your shoot your flare, Brigade back up will start pushing to the Memorial. Here is 3 ways they are coming from. If you have 3 people in total, just guard this paths. It's much easier this way. At least 2 groups from each side will spawn. Around 14+ will try to take you down.
Left gate.
Main gate.
Right side path.
If you playing solo. It's a smart thing to hide inside vault and kill enemies as they try to get in. Or just stand your ground as an epic gamer warrior. (But you probably will die at least once doing this).

Walkthrough video.
Codes.
https://youtu.be/b0nfc50EmwI
Lincoln Memorial.
https://youtu.be/2rz7IvglAbY

Playing solo is fun, but when it comes to securing loot from Join or Die mission it can be a real hustle or even can put a stop sign to your whole team.
What you need to do is run outside, clear some walkers and turn left to sandbags at the edge. From this edge you will be able to throw all your hard earned weapons to the roof of this truck.
Just run back and forth and throw all good stuff you found to the roof. If something will fall down, not a big deal. You want them down there anyway later on.
When everything is in extraction area. Make yourself ready for a small hustle. What you want to do is to wait till all walkers stuck around ladder and around military truck. So throw everything down, bacause you will not be able to get up there again. Small reminder: You can't kill every walkers in the horde. They will respawn as fast as you will kill them.
Area behind Military truck close to the wall is safe to you to attract walkers.
The pattern for securing loot will be:
1) Run to the car and drop the loot inside.
2) Run back, get the bag on your back and make some noise behind the truck. Wait a little and make your way back to the car.
3) Repeat.
You can use your Molotov to kill and hold some of the walkers when you running back and forth with your loot.
Quick tip: If you skilled your Mark for Death to give you a speed boost, use it as you run around. Mark nearest walker, smash it and "gotta go fast", boy.
You don't need to throw last bag inside the truck, it will count if you keep it on your back.
After you secured all goods, just hold 5 seconds and you just successfully done Join or Die mission solo with ease.

Walkthrough video.
https://youtu.be/N6pnE7LvK0k

First of all, I want to repeat myself, that you don't have to follow this patterns one on one. You can play your game whatever you like.

I want to thank Chakki and †bLaDe† for playing with me and sharing their initial game tactics with me.
And I want to thank Sylvanas Windrunner for editing.

I also want to point out two guides that will help you to locate all loot crates around this mission and understand stealth mechanics of this game.

Loot crates

Game mechanics

Thanks for reading. Hope this guide will help you enchant your game experience.