[RayChuang88]

The problem is that unless you use a pretty powerful nuclear device (at least in the 300+ KT range), EMP is not as effective as people think. I think that was why the Russians maintained a number of obsolete SS-9 Scarp (R36) missiles in service (long after they were made obsolete by the later SS-18 Satan (R36M)), which had a 20+ MT nuclear warhead that could generate an enormous amount of EMP specifically to knock out large fractions of the American power grid.

[RFEngineer]

“The problem is that unless you use a pretty powerful nuclear device (at least in the 300+ KT range), EMP is not as effective as people think.”

This is incorrect. Emp is remarkably consistent. A 10kt nuke provides only a marginally smaller emp than a 300kt. Gamma yield is what drives emp. A hydrogen fusion weapons. Does not have a gamma yield greater than a smaller fission weapon.