Several posters cite the uncertainty of response as strengthening the deterrent value of a national nuclear capability. That is neither logical nor credible.
It is actually logical.
And it doesn't just apply to the deterrent. As an example people are advised to keep their car keys out of sight from external observers. The reason being that providing a perpetrator certainty as to their location allows them to exploit that knowledge to evaluate the effort/risks in overcoming your security based on the confidence of acquiring them.
So uncertainty can increase the effectiveness of your security.
As it can increase the effectiveness of your deterrent.