Wild Card: You and What Army is started by talking to Yes Man in the rear of Benny's presidential suite on the 13th Floor of the Tops Casino.
The bunker is inside the weather station at the Fort. To gain access, have Caesar give you an optional part of the quest: to find the bunker and destroy it. If you accept, he will let you enter, at which point you can either destroy the army or activate it; Caesar will assume that the rumbling of the army activating was whatever you used to destroy it.
Option 1: Upgrade Securitrons
Traverse the Securitron vault and enter the door labeled "Computer Room Door." It can be found up the stairs in the hallway farthest west. Insert the Platinum Chip into the Securitron Operations Console.
Option 2: Disable Reactors
To disable the reactors, simply fire one round into each of the 3 reactor modules.
(Optional) Upgrade the Securitron army, to use later for your own purposes.
4
(Optional) Destroy the Securitron army by overloading the bunker's reactors.
Notes
Inside the Securitron vault there is a constant +1 RAD.
Mr. House tells the player he cannot control anything in the vault and asks if you want you can disable the security, which would make one think he should have a password for the computers to disable the robots, and turrets, but does not offer one.
If you agree to "destroy" House's robot army, you'll get your stuff back inside the Weather Station, your belongings will be taken again once you are out.
If you want to work with the NCR and you work with Yes Man for too long, Don't Tread on the Bear will automatically begin. Complete one more quest for Mr. House or Yes Man, and the NCR won't give you anymore quests and any NCR quest active will fail.
The Fallout: New Vegas Prima official game guide incorrectly states that Yes Man's picture will be on the computer monitor if you have installed his AI into the Lucky 38's mainframe. The screen in fact remains blank. However, once all the Securitrons inside the bunker have been upgraded, Yes Man's face does appear on the screen.
Bugs
PC If you pass the Speech check for meds with the guard at the front gate, your weapons will not be confiscated either. This leads to becoming trapped in the weather station, with the guard saying it's okay to leave but not actually unlocking the door. Excluding console commands, the only way to get out is to sneak attack the door guard and take his key; a good position for the sneak attack is the stairway leading to the vault, as the Praetorian guards can't see you no matter your Sneak skill. (FIXED v. 1.4)
theres also the bug where u cant talk to caesar (it zooms in on him for 3 seconds then zooms out) causing the platinum chip to be lost causing you to get really pissed off.