Mission: Countdown

Mission: Countdown Alpha, Mission: Countdown Bravo, and Mission: Countdown Charlie are repeatable main quests in Fallout 76 which trigger a nuke launch upon a map location selected by the player, creating a blast zone.

Detailed walkthrough
Before starting this quest, the player character will need to acquire at least one nuclear keycard and the decrypted weekly launch code for a silo bunker.

Upon entering a silo bunker (either Site Alpha, Site Bravo, or Site Charlie), be prepared for many robot enemies, mainly Protectrons, Assaultrons, and Mister Gutsy robots of the Lieutenant, Major, and Colonel rank. Bring energy-resistant gear and energy weapons, along with ballistic-resistant gear to protect against Mister Gutsy robots, which use armor-piercing double tap ballistic weapons, and Assaultron Dominators, who use assaultron blades in close-quarters combat. Both enemy types can whittle down health in a short period of time if they are not dealt with quickly. A highly radioactive room will also be within the silo, that being the silo's power chamber with its primary and secondary reactors, so bringing radiation protection is recommendable.

The first part of the quest will require the player character to find a way past the first set of laser grids, by means of forging a biometric ID card. Old biometric ID cards can be found through the door to the left after first stepping out of the elevator. The majority of the silo will be filled with laser turrets and robots, but with a Level 3 hacking skill, and using terminals scattered throughout, the robots and turrets can be programmed to shut down or by removing targeting restrictions, made to turn on one another. The robots that can be deactivated include the Robobrains serving as the area commanders, such as the Residence Assistant and Launch Commander Robobrains. The initial starting room, serving as the residential area of the silo, will have a few Mister Handies to deal with before the Mister Gutsies start to appear from the robot fabrication tubes in some of the rooms.

In the next room are two terminals that the player character must read to acquire information on security protocols, giving instructions for creating new biometric ID cards. After acquiring an old biometric ID Card, the player should locate an ID card eraser and follow the instructions on the terminal. Afterwards, following the mission markers will take player characters to biometric scanners in the medical room which they will enter. Then, a nearby terminal will fabricate the new card. Activating the card will deactivate the first laser grid.

Through the deactivated laser grid and the silo corridors is the Power House and another terminal to handle the robots and turrets. Here, the player character should locate a terminal with instructions in the room with the nuclear reactors. Using the terminal will shut down the reactors for 3 minutes and allow the player character to repair sections of piping around the room marked by yellow and black stripes that are cracked and hissing steam from them. These repairs do not require any materials to complete. Prepare to deal with radiation from the reactors, as well as a variety of robots that will periodically spawn, including utility Protectrons armed with nailguns that work like railway rifles. Once the reactors restart, either manually or automatically, the quest will proceed to the next stage.

In the next stage of the quest, the player will follow quest markers to the control room, where they will need to destroy dozens of mainframe cores. Destroying the cores in one room will deactivate nearby laser grids and grant access to more cores and laser grids. There are more terminals with aforementioned robot and turret controls, but the player character should be prepared to fight higher level robots such as Assaultron Dominators and Major/Colonel Gutsy in the main mainframe room. After destroying all cores, follow the markers to the next area.

The following stage of the quest involves crafting 15 replacement mainframe cores or finding intact ones around the room. Repairs can be made at a nearby tinker's workbench with circuitry and steel. Replacing all 15 cores and using the terminal to open a security door will take the player to the launch silo and the final part of the quest. There is also a terminal needed to open a shortcut from the entrance straight to the storage area, bypassing most of the silo explored earlier if killed and needing to retrace steps to where the player characters died. One should also watch out for a Sentry Bot in the storage area, who is patrolling alongside the usual Protectron, Assaultron, and Mister Gutsy robots.

Inside the launch silo is a nuclear missile. Past this, through a door and up a few flights of stairs is the Launch Control Center. The player character will be prompted to initiate launch prep. Doing so will spawn friendly launch control robots which must be protected as they carry out their corresponding tasks. Each Crew Chief is a Protectron with various robot parts attached to the head, torso, or legs, such as the head of a Mister Handy or Gutsy for the Launch Control Chief, Sentry Bot upper body for the Chief Propulsion Officer, Assaultron head for the Chief Telemetry Officer, Robobrain torso for the Chief Targeting Officer, and Assaultron torso for the Chief Guidance Officer. This process tends to be rather tedious, with the robots being slow moving and the enemies numerous, especially Assaultrons, Robobrains, and Mister Gutsies with their head lasers, melee strikes, Tesla weapons, smokescreens, and armor-piercing double-tap ballistic weapons. Successfully defending the Crew Chiefs will complete the quest. If any robots are destroyed, use the nearby robot fabricators to create new ones to replace them. As long as one is intact, launch prep will continue, but at a slower pace until at least two are working the prep work again, and be paused completely if all the Crew Chiefs are destroyed until one is rebuilt. Once launch prep is complete, any remaining security robots that were still active and trying to stop the preparations will be immediately killed off since the silo is now armed and ready to fire.

Once the quest is completed, the player character will be prompted to select a blast zone target location within Appalachia for the nuclear missile. Some lower-level areas located in the western portion of Appalachia are considered to be within a "protected zone" and cannot be targeted. If fissure site Prime is targeted, the scorchbeast queen will be spawned and the Scorched Earth event will begin. If Monongah Mine is targeted, the event A Colossal Problem will be triggered. Targeting other locations will spawn higher level versions of whatever enemy is normally present in that area.

Rewards

 * 50 XP is rewarded upon completing each step of the quest: Residential, Reactor, Operations and Storage.

Bugs

 * Robobrains spawned during the Launch Prep Sequence will not grant any experience points or loot.
 * Rarely, the Launch Prep chiefs will not contribute toward the progress bar.
 * Leaving and re-entering the silo will reset their placement and may restore progression.
 * Occasionally, all robots and turrets will immediately die as the player approaches them.