Edit - I wrote this guide when Discovery Mode hadn't been added to the game, this solution is for clearing the Raid on Normal difficulty. From all the comments I'm guessing Discovery Mode is significantly easier to complete.
Now on to the actual guide.
Before you can even join the raid, you will need a minimum Gear Score of 490. So before you try to join a raid you'll want to focus on hitting that minimum requirement. Before most groups will even ALLOW you to join, you will need a high DTE stat. On your stats page for your character, in the Offense tab you'll find a stat called Damage To Elites. I've seen groups require a minimum of 70% DTE regardless of whatever else you have in your build, and this is only partially due to elitism, the rest is due to the sheer number of Elite enemies you'll face in the raid. So having this stat as high as you can get it will help you in the long run. Also, put as much as you can into weapon damage and damage to armor, as only a handful of enemies in the raid don't have armor.
One of the raid's mechanics is the disabled radar and that each player is limited to reviving another player from death ONCE per encounter. So running the blue Hive skill will be in your best interest for much of the raid as it will revive you if you are downed so long as you go down while still in cover.
The first boss you'll encounter is a big dude in heavy self-repairing armor named Boomer. His boss room will have two mounted turrets that you'll need to both make him vulnerable and actually down him to damage him. On his chest is a self-repair module, and keeping it damaged so it cannot activate and heal him is a must. Also in this room are four computer towers that can only be damaged by the nearby mounted turrets. While the towers are active, they will emit a blue aura that will make any enemy in their vicinity immune to all damage, so keeping the mounted turrets from being damaged is required or the encounter will fail. In fact, if both turrets are destroyed the encounter will reset itself. Defeating Boomer will require a balance of dealing with the extra enemies that spawn in this area, one person damaging Boomer while keeping his self-repair module from activating and luring him near a mounted turret but getting him to turn his back to it so the person operating it can damage his backpack enough to stun him so he drops to one knee. This is the damage phase, the ONLY time you can actually damage him. In addition, there are a series of laptops in this area that can disable the nearby computer towers to prevent them from reactivating. The nearby monitor will tell you which laptops, labled A, B, C and D, need to be interacted with in order to shutdown their restart process. This will prevent any of the enemies in the room from being immune to damage. Once Boomer's damage phase is finished, he will launch an EMP grenade at whichever mounted turret you used on him, so the most effective method is to rotate around the room while dealing with the additional enemies that spawn and ONE person keeping Boomer's aggro and luring him to the other mounted turret. The player with his aggro will have a red eye icon on their name and outside of the damage phase when Boomer is downed after damaging his backpack with a mounted turret, no one else should be attacking Boomer aside from helping the player drawing his aggro deal with the self-repair module on his chest.
After dealing with Boomer you'll come to an airplane hangar where you'll deal with Ricochet and Dizzy, each is a heavy with a minigun and will spawn in both halves of the hangar. You will need to split your group up to deal with each of them as both halves of the hangar are physically cut off from one another. The bosses are straightforward enough, even with the additional enemies that will spawn from the nearby windows. 3 players on each side will need to trade aggro and dealing with the extra enemies while the 4th player on each side have to complete a minigame with the computer terminals in the middle of the room to keep poisonous gas from killing everyone as the gas will damage your health bar directly and ignore all armor. Communication is key, as the two players dealing with the computers have to coordinate with each other and hit the correct computers in sequence. Also, bear in mind that once either boss is taken down a THIRD boss in this room will appear, named Weasel, he's just another heavy with a minigun and an absurd amount of armor. It will be in your group's best interest to take down Dizzy and Ricochet nearly at the same time to prevent one group from having to deal with TWO bosses at once.
After the hangar section, you'll come to a mall area where you'll deal with two robot dogs on steroids, Buddy and Lucy. Lucy has grenade launchers and a 360 degree minigun that can down you in one shot, Buddy has a self-repair function along with a rail gun and several seeker mines that do minimal damage but WILL force you out of cover. Like the other bosses, one player will have their aggro and this will be indicated by a red eye symbol by their name. There is a blue room in this area, this is the area you want to drag Buddy into while dragging Lucy to the other, this will ensure that the group dealing with Buddy will not have line of sight with Lucy so her 360 degree minigun attack won't down them while they're trying to deal with Buddy, so the Lucy group will HAVE to indicate when she is readying this attack. The tricky part with this fight is that while the two miniature Metal Gears don't share a health bar, they sync up, and if one is pushed past a threshold on their health bar before the other, it will trigger their overdrive and they will want to rush toward the center of the room so they can heal each other, so both groups will need to balance their DPS to make sure both miniature Metal Gears are being damaged at the same pace, and if you see either moving away from your group toward the middle of the room to get close to each other, this is when you need to pour on the DPS to get their aggro back. Also, make sure you destroy Buddy first, as if you destroy Lucy first, Buddy will trigger his self-repair module into overdrive and you will no longer be able to damage him. One helpful tip is that the purple Chem Launcher will deal with Buddy's seeker mines before they deploy. Just don't go overboard with it or it will hide him in the smoke and your teammates will have trouble targeting him. When Lucy is readying her 360 degree minigun attack, Buddy will sync up with her and deploy seeker mines, one shot of the purple Chem Launcher will do enough damage and last long enough to destroy his seeker mines before they launch and have a chance to damage anyone. Keep the two robot dogs in sync until Buddy is one bar away then proceed to melt him down. Once he's down, deal with Lucy while making sure NOT to accidentally get killed in the process and you'll have another boss dealt with. Another strategy is to lure Lucy into the blue room and lure Buddy into what is effectively called a "triangle" room. From the entrance, look immediately to the left, the room in question will be the one on the right when facing left from the entrance of the room. When done correctly, Buddy will effectively get "stuck" in this room and will not move at all.
The final encounter will be Razorback, a giant drone launching truck. This boss is extraordinarily complicated, but if you're running with a group who all know their jobs then it will make it much simpler. Before engaging anything, clear the adds in this area. For this encounter, you'll want to have four players run add control, while the other four will run the generators. When adds appear, when Razorback launches drones, and when the heavies appear, it will be the job of the add control to deal with them as quickly as possible. Of the four on generators, at least two must have a crossbow, more on that in a minute.
To begin the encounter, you'll need one person to direct the generator team to step into the white circles around the four numbered generators at the same time. You'll see a percentage gauge appear over them, when they reach 100%, Razorback will open it's top and launch drones, when this happens, the add control who have line of sight will want to open fire on the drones launching, not to try to destroy them, but damage them just enough to draw their aggro away from the generator team. Another effective strategy is a grenade launcher, one well placed shot will destroy all the drones launching from Razorback before they have the chance to damage anyone. Once the generators reach 100%, Razorback will open two small panels, one in the front and one in the back, both with a red light in them. One crossbow per side needs to fire a shot to destroy the grate protecting this opening, after this, the other generator player needs to throw a grenade, not a fire grenade mind you, into the opened grate. Once both have been blown up, the display over the four generators will disappear. This is the ONLY time during this phase that the four generators should move away from the generators. Once this happens, the four generators need to move to the front of Razorback and open fire on the two small 'wings' that appear at the bottom of the massive back panel that it raises when launching drones. When both wings are destroyed, it will reveal a weak point in the middle of the massive back panel, deal as much damage as possible to it before it covers the weak point. Once enough time has passed, Razorback will seal it's roof again, regardless of whether or not your team destroyed both wings. When this happens, it will launch missiles toward the generator players, indicated by red lights appearing on the floor. Dodge these as quickly as possible.
After each damage phase, a heavy will appear at one of the four corners where the four missile launchers are situated. You will hear a siren when this heavy is trying to activate the missile launcher, the add control needs to keep an eye out for this and IMMEDIATELY make it known where the heavy is and pour as much damage as possible to defeat them, as if they activate the missile launcher the entire team will die and the encounter will fail. As the encounter drags on, robot dogs will also appear, calling them out to help defeat them as fast as possible is critical. While there is no 'time limit' to this fight, as it drags on, more heavies and robot dogs will spawn, you'll go from having to deal with just one, to dealing with two of each after each damage phase, so defeating Razorback as quickly as possible is essential.
After enough damage is dealt to the weak point on the front of Razorback's massive roof panel, the same generator process needs to be repeated, except the new weak point will be on the BACK of Razorback's roof panel. There will be two weak points that need to be destroyed each damage phase to make the real weak point vulnerable to damage. Repeat the generators and clearing heavies and robot dogs until the center weak point on both sides of the roof panel are destroyed. At this point, all four missile launchers around the arena will activate one after another, each generator and add control player needs to be united and standing by at the control panel for each missile launcher. The second the panel comes online and becomes vulnerable you NEED to open fire and destroy it before the missile launcher fully activates and fires, or the entire team will die and the encounter will fail. Once all four missile launchers are permanently deactivated, Razorback will blow up and you will win. The Achievement will unlock shortly after that.
Also of note, are the four raid keys you can find throughout the raid. One is found after Boomer and before the hangar where you fight Dizzy and Ricochet. One is behind a locked door you need to throw a grenade through to open after this fight. One is in an elevator before Buddy and Lucy, and the last is in front of the windows before Razorback. After you've defeated Razorback the chest you use the keys on will be in an open cargo airplane in this arena behind Razorback.
Have patience, coordination, and the best gear you can find outside the raid, and this Achievement will be yours.
Good luck out there Agents.
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