When you completed Episode 31 you can build a Nuclear Weapon for 750.000 GMP, 75.000 Fuel and 50.000 Metal. It about (real) 26 hours to complete (depending on your Base Development Unit Level). You also lose 50.000 Heroism Points (you need 150.000 for the Hero Achievement). I highly recommend you no use waste that kind of Fuel, if you haven't upgraded your Motherbase fully yet.
If you have a Nuke, your FOB can't be attacked by Players who don't have the Hero Status/Achievement. The Nuke can be build from the Menu
-> Motherbase -> Resources ->
---- After Patch 1.04
You can't use Offline Ressources anymore to build the Nuke, now you need processed Online Materials. They can be farmed by playing Dispatch and FOB Missions. If you switch to Offline Mode you can still build them with offlineMaterialsPosted by LAZY SHIKAMARUX
: I found out a good way to pass the time while it's being built. If you go to your power settings and turn off your consoles ability to turn off after inactivity, you can snap an app while playing the game. While the app is snapped if you have your controls focused on the snapped app, you can turn off your controller and the game will still run without prompting you to plug in a controller.