“America sleeps in the Divide - giants, beneath the earth. You saw one locked in the silo beneath you. There's more. Only takes a few of them, locked below ground, to tear apart the earth... and cast dust, sand... ash... into the skies above.”— Ulysses
This quest appears after the Courier deals with Ulysses and decide the fate of the nuclear missiles at the temple. Choosing any option other than canceling the launch begins this quest and fails The End. Leaving the temple and watching the DLC ending completes the quest. On returning to the Mojave after the ending slides, a nuclear explosion can be seen in the general vicinity of whichever territory was targeted (or both, if the player character chose to nuke both Legion and NCR).
Run for the Canyon Wreckage.
Optional: Deliver Ulysses' last message.
The only place where ghoulified Caesar's Legion members can be found is at Dry Wells, if the Courier have directed the nuke to Legion territory (except for the marked men).
Nuking a faction will drop the Courier's reputation with that faction down to the lowest possible rank (Idolized will become Wild Child, while Liked will become Soft-Hearted Devil). However, it will not turn that faction hostile towards the player character, even if their reputation drops to a rank (i.e. Soft-Hearted Devil) which would normally trigger hostility. This can lead to the bizarre situation of Legion assassins or NCR hit-squads tracking them into the wastes, running up to the Courier as if to attack, then simply standing around or running away again. However, if they subsequently return, they may turn hostile.
If one completes the quest before confronting Benny, their Legion infamy will be removed after speaking to Vulpes Inculta or Alerio, meaning the player character can still secure a positive reputation with the Legion after targeting them.
If one completes the quest before starting the NCR quest Things That Go Boom, their NCR infamy will be removed after speaking to Ambassador Crocker and agreeing to help him. This means the player character can still secure a positive reputation with the NCR after targeting them.
Both The Apocalypse and The End have the same rewards (apart from the fame/infamy gains). However, with The Apocalypse, the player character gains access to the Long 15 and/or Dry Wells, and their subsequent loot. Nuking both yields the most potential rewards.
Everything that ED-E is carrying will be returned to one's inventory after the quest is completed.