It can be found in an Average locked footlocker in Colonel Autumn's quarters at Raven Rock - level 2 (west 2C), and can be used to initiate John Henry Eden's self-destruct sequence during The American Dream.
I'm not entirely sure Eden can be trusted. And I think he knows I don't trust him.
But I don't think he knows I have the emergency destruct sequence for his console.
"Priority Override, Authorization code 420-03-20-9" and... boom. It'd have to be a last resort, of course, but at least the option is there.