What's The Point Of Nuclear Weapons On Instant Alert?

Nuclear missiles "on alert" could too easily be launched by mistake

From New Scientist:

IN THE next few weeks, President Barack Obama will publish his delayed Nuclear Posture Review (NPR), setting out the role nuclear weapons play in US defence. This is Obama's opportunity to end one of the most dangerous legacies of the cold war: the nuclear missiles the US and Russia keep ready to fly in minutes. The signs are that he is unlikely to take it.

This leaves the questions why does the US keep its nuclear weapons "on alert", and are they really needed?

Read more ....