This is a VERY abbreviated and simplified explanation of how things work.
In the bad old days (Think "War Games" era), in the event of an accidental nuke, a percentage of silos would launch automatically to insure that if we didn't win, no one else won.
Then cooler heads prevailed and we disabled most of the "auto-launch" functions. Not all. We had that infamous event where a launch crew got a real launch order, and refused to turn the keys. Which was good, because the test computer that issued the command randomly and accidentally actually transmitted a real launch code by mistake.
Now, in more enlightened times, we have an almost foolproof system of checks and balances to prevent world wide conflagration in the event of an accidental nuclear detonation.
The only problem is, that under a couple of former Presidents, maintenance of the nuclear arsenal was so sorely neglected, that should the order come to launch, most of the nukes will detonate inside the silos.
And that's what happens if the Tactical nuke in the self storage unit should accidentally go off.