After you have finished Officer On Deck and I Am Become Death Quest, and get the Nuclear Keycard and a complete Nuclear Launch Code, then it’s time for you to start off the Mission: Countdown Main Quest and launch a nuke. This quest might seem confusing for players,especially new ones. To save you time, we made this Mission: Countdown guide to help you complete it more easily. So just keep on reading.

 
Mission: Countdown Quest Overview
 
1. Complete Chapter 23 'I Am Become Death' up to the Objective, 'Launch a Nuclear Missile'.
2. Either boldly solo this Chapter, or recruit a team to help you. If you work as a team, make sure everyone knows what to do and how to do it.
3. Each Silo has five events. You need to complete these in order to gain access to the Launch Control System. Basically, each of the five events requires you to hold your line against a never-ending stream of monster robots. Good luck.
4. Also, keep in mind that you shouldn't try to kill every monster. They are literally unending.
5. Basically, you're going through a dungeon. There isn't anything special, other than it will be hard. So be prepared.
 
How to Complete Mission: Countdown Quest?
 
To activate the Fallout 76 Mission: Countdown main quest, you finish I Am Become Death quest in chapter 23 first, so that you can get a complete Nuclear Launch Code. With this done, it is time for you to launch a nuke. There are totally three nuclear missile silos in the game and you only need to access one of them. Since each Nuclear Launch Codes is specific to one of the three silos, so you need to head for the one that the mission will mark for you. All three are in the Savage Divide, but in very different parts of the region. Here are specific locations of each nuclear missile silos.
 
1. Site Alpha is close to the middle, southeast of Top of the World.
2. Site Bravo is further north, situated south and slightly west of the Palace of the Winding Path. 3. Site Charlie is in the south, lying due west and slightly north of Fort Defiance, on the opposite side of the Savage Divide.
3. Site Charlie is in the south, lying due west and slightly north of Fort Defiance, on the opposite side of the Savage Divide.
 
Since each of the above Sites is heavily defended by high-level robots, so, bring your best weapons and prepare your inventory and yourself. Don’t have powerful weapons? Come and buy Cheap Fallout 76 Bottle Caps at 5mmo.com. In each silo you’ll have to progress through five events, which challenges you to hold your line against a never-ending stream of monster robots, so it would be much better if you work with a group. After all, it is too difficult to complete objectives while fight waves of additional powerful robots.

 
 

Once you complete all five events, then you’ll access the control system. Put your Nuclear Keycard into the terminal to activate it and then input your Nuclear Launch Code. Beware, if you mistype the code, all of your effort will be wasted unless you have spare Nuclear Keycards!  after inputting the correct code, you’ll enter a targeting computer and can choose a spot to launch your nuke. Once you fire, the quest will complete and you’ll start “Death From Above!” the follow-up main quest.