Unless we have President Obama, in which case he would fall to his knees and beg forgiveness of whoever did that to us, apologize for whatever we did that made them so angry, and vow to pass legislation to compensate them for any harm we had caused.
Correct. An EMP weapon has never been used, the best we have is educated speculation. It would be effective but not nationwide
but I know for a fact that American weapons systems have been hardened for years against this possibility. We would know who did it (terrorists don't yet have the capability to detonate an EMP weapon over Iowa, and won't for years) and I'm sure would retaliate in a way that the perpetrator would never forget.
No retaliation would be possible if EMP armed cruise missiles were fired from ships off the East Coast that would be scuttled and sunk after firing off the missile. One EMP missile each for New York, Washington, Boston would create plenty of chaos
The energy to do national damage would require a multi-megaton warhead. A nuclear warhead detonating on or above the US will result in a response the sender does not want to contemplate.
Washington State Department of Health
Office of Radiation Protection
Electromagnetic Pulse (EMP)
What Is EMP and How Is It Created?
The most important mechanism for Electromagnetic Pulse (EMP) production from a nuclear detonation is the ionization of air molecules by gamma rays generated from the explosion. These gamma rays ionize the air molecules by interacting with the air molecules to produce positive ions and recoil electrons called Compton electrons. This pulse of energy, which produces a powerful electromagnetic field, particularly within the vicinity of the weapon burst, is called an electromagnetic pulse. EMP can also be produced from non-nuclear sources, such as electromagnetic bombs, or E-bombs.
High-altitude nuclear detonations and electromagnetic bombs can generate EMP that has the potential to damage or destroy electronic devices over widespread areas. Electric power systems would also be at risk from surges produced by such weapons. However, the EMP from a kiloton-range surface nuclear explosion would not be expected to produce serious damage outside the radius of severe destruction from blast.
A 1.4 Megaton bomb launched about 250 miles above Kansas would destroy most of the electronics that were not protected in the entire Continental United States. During the brief return to atmospheric testing in 1962, a 1.4 megaton nuclear weapon was detonated over Johnston Island at an altitude of about 250 miles. The effects of EMP were observed in Hawaii, 800 miles east of the detonation. Streetlights and fuses failed on Oahu and telephone service was disrupted on the Island of Kauai.
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http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-htm/fs41elecpuls.htm