alt Hacker NewsContainer ships tend to be fairly slow to respond and may not function as expected during a nuclear war.
The only way for this to work as a retaliatory measure is to have the weapons already in place at the target locations. Now, imagine if someone were to discover the weapon and trace it back to whomever installed it. This is effectively a slow motion nuclear exchange that was initiated by the "defender".
The point of this particular sort of deterrence is to prevent a decapitation strike by an opponent who thinks they can knock them all out.
"Yeah, you can drop bunker busters on the silos you know about, but six months later one of your cities evaporates."
The five big nuclear powers use subs for this, but it's hardly the only option.