>>7
No, the shield doesn't have to be perfect, actually. It just has to make the enemy think that a first strike would not effectively destroy all the other side's nuclear arsenal.

You're thinking "Cold War," anyway. Such a system would not be intended for use against Russia. The Russians are our friends, more or less, at least for the moment. It'd sure make a lot of assholes pucker in Beijing, Pyongyang, and Tehran, though.

It doesn't even have to work, really. It could be cardboard mockups with tinfoil glued on them to make them look all ZOMG L33T SPACE AGE and if the enemy believed they were real and would work, that'd be good enough.