Before the Great War, the automated defenses of the silos would protect them from anyone without a Missileer escort. Since Missileers are an extinct species, if the Vault 76 dwellers want to gain nuclear capability, however briefly, to fight the scorchbeasts (or each other), they need to do it the hard way.
This is the penultimate challenge in the game, second only to Event: Scorched Earth. It requires a massive supply of ammunition, stimpaks, and spare guns, as robots spawn constantly during a silo event and players are required to complete five separate events to gain access to the launch console. Soloing the silos is doable, but has no special rewards.
In general, preparations should focus on bringing fully repaired weapons and armor, several hundred rounds of ammo (thousands if need be), a spare gun, stimpaks aplenty, RadAways to remove radiation, and any buffing consumables.
Weapons are best modded with armor piercing modifications or legendary effects that ignore armor. Robots are heavily armored.
Spare components for repairing gear is also a good idea, as they are scarce in the bunker. Since radiation is present, a hazmat suit will definitely help in surviving the trickier areas.
Explosives are good, especially of the pulse variety. Mininukes, due to the short ranges, are only advisable if ducking and covering is second nature for the player.
45 steel and 30 units of circuits are necessary for the Storage Area event. Bringing them in advance really, really helps.
At least one player should have level 3 hacking and lockpicking. The former allows for skipping one of the event, the latter gives access to more supplies on the way.
Clear every room before attempting an event. That includes any turrets that can't be hacked or switched off and any robots. As the endless spawns do not begin until the event starts, this gives time to repair, resupply, and heal up (and hack).
Hack everything. There's no penalty for hacking terminals and only boons. Players can enable friendly robots, frenzy turrets to attack hostile robots, deactivate robobrains, enable decon arches in the reactor areas, and so on, and so forth.
Don't get swarmed - prioritize. If you see an Assaultron, drop everything and junk it. The head laser is a real annoyance under the best of circumstances and in confined spaces it's absolutely brutal.
Don't leave the silo unless you want to abandon the quest entirely. Personal progress resets after a few moments outside. Group progress resets completely if the whole team leaves.
Always open the shortcut from the Storage Area to the starting chamber, to avoid being forced to redo everything if a player drops or the team is wiped out.
The first step in tackling the silo is the residential area. Each player needs to complete this section, which requires the player to create a biometric ID card at the marked terminal, using an old biometric ID card, erasing it, rewriting with player data, and registering it.
The terminal in the entryway allows the player to disable the supervisor and the turrets, which is of immense help. A good strategy while everyone is trying to get registered is to do it in pairs: One player goes through the motions, the other watches their back.
The reactor seems to have been built by the lowest bidder and is locked down due to a hazardous radiation leak. That's why players need to pack radiation prophylaxis, RadAway, or hazmat suits and power armor.
The goal is to end the reactor security lockdown. Players who have maxed out hacking and lockpicking can simply pick the look on the door in the heart of the reactor sector, then hack the security command terminal (Bobblehead: Science helps) to lift the lockdown, skipping the event.
Otherwise, players need to go through hoops. First, the terminal in the entrance area can be hacked to disable the turrets, supervisor, and activate the decontamination arches to free up RadAway (though not healing sadly). Second, other terminals in the area can release friendly robots to help.
To repair the reactor and lift the lockdown, players need to turn it off, repair the pipes, and reactivate it. Shutting down the reactor activates the security alarm, so players should take position and spread out - preferably by the broken, leaking pipes. Then it's a matter of quickly repairing them and restarting the reactor to end the lockdown.
Quick and dirty: The security alarm goes off as soon as the players step foot inside ops. The robots will swarm. The terminal in the first room allows for disabling the robobrain and the turrets, as usual.
The goal here is to destroy the mainframe cores. Explosives work wonders in confinded spaces and can accelerate the dismantling procedure quite a bit. The event and the alarm goes down as soon as the last core croaks.
The storage area is a breather, mostly. The first office on the side leads to the usual supervisor/turret disabling terminal. The security alarm won't trip until the players interact with the security mainframe or the cores inside. It's a good idea to take time to clean up, open up the shortcut to the entrance hall (locked terminal), repair and resupply. Unlike in most locations, setting the turrets and the Robobrain to attack everything is a sound way to clear the way forward.
The goal of the event is to repair 15 damaged cores from the mainframe by the security door (each requires 3 steel and 2 circuitry), then slot them in so that the mainframe will open the security door. One player should grab them all, gather the resources (or carry them already), repair them at the tinker's workbench, then slot them back in for a quick finish.
Alternatively, players can collect spare cores spread out across the storage facility. They are usually hidden in various boxes, sit on shelves, or otherwise placed in a (fairly) obvious area.
The final stage of the silo mission means going through the control room. This is a defend event, where the players need to protect all section chiefs as they prepare for the launch. Since the security alarm won't activate until the launch procedure is initiated, there's time to go through the area meticulously, lay mines, use the terminal to disable the robobrain and turrets, etc.
The launch prep releases the robotic section chiefs to complete their procedures. Defending them can be tricky, but as long as the Launch Chief remains active, the procedures will continue - other section chiefs just accelerate the process. The moment the launch prep is completed, the quest ends.
Where to nuke?
The final step requires players to insert the nuclear keycard into the receptacle, input the silo code, and select the target. Note that any failed code attempts will still consume the keycard.
Nuclear keycodes can be painstakingly deciphered by completing Hide and Seek and Destroy, collecting dead ghouls, or simply visiting NukaCrypt, which contains the weekly nuclear keycodes.
Picking the target for nuking requires players to pick a location across Appalachia. Most major areas can be nuked, except for the Forest around Vault 76, with fissures the suggested target. The Whitespring Resort is frequently nuked, due to the abundance of flora nodes (which transform into mutated flux flora), ease of access to the Congressional Bunker and its decontamination machines, and the proximity of the merchant mile with its crafting stations and shops.
Nuking any non-fissure target will spawn a special holotape from the Overseer at the Site Charlie cache.