The term electromagnetic pulse (sometimes abbreviated EMP) has the following meanings:
- A burst of electromagnetic radiation that results from an explosion (especially a nuclear explosion) and/or a suddenly fluctuating magnetic field. The resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges.
- A broadband, high-intensity, short-duration burst of electromagnetic energy.
In military terminology, an EMP bomb detonated hundreds of km above the earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. Nuclear electromagnetic bombs have three distinct time components that result from different physical phenomena. Effects of an EMP device depend on the altitude of the detonation, energy yield, interactions with the earth's magnetic field, and shielding of targets.
The fact that an electromagnetic pulse is produced by a nuclear explosion was known since the earliest days of nuclear weapons testing, but the magnitude of the EMP and the significance of its effects were not realized for some time.
During the first United States nuclear test in 1945, electronic equipment was shielded due to Enrico Fermi's expectation of an electromagnetic pulse from the detonation. The official technical history for that first nuclear test states, "All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment."During British nuclear testing in 1952–1953 there were instrumentation failures that were attributed to "radioflash," which was then the British term for EMP.
High altitude nuclear tests of 1962 increased awareness of EMP beyond the original small population of nuclear weapons scientists and engineers. The larger scientific community became aware of the significance of the EMP problem after a series of three articles were published about nuclear electromagnetic pulse in 1981 by William J. Broad in the weekly publication Science.
EMPs on Doomsday
On September 25, 1983, the first missile launched towards the Soviet Union was a high altitude ICBM that reached into low earth orbit. The orbit, though was over twice as high as the Salyut 7's apogee. The soviet space station, though was not in its direct path. The horror of the events, though, did unfold before the eyes of its soviet crew. The crew found themselves cut off from communications with ground control in most of the USSR, though they did make contact with stations in Siberia after all the bombs had fallen. That communication was in snatches, though, due to the chaos in western Russia.
It would be months before any survivors from the Moscow area would make contact with party loyalists in Siberia. Within months after this, the intact communications systems on both sides of the Bering Strait would result in rescue operations (which turned into a de facto military takeover) in westernmost Alaska.Before the missile reached its appointed target over the Ural Mountains, though, two soviet missiles reached an easier altitude of about 120 miles above Indiana and Colorado, knocking out all unshielded electronics from Hamlin, Maine, to San Diego, California. As population centers crumbled and millions died, the survivors were left "blind and deaf" electronically. Towns and states were in chaos, unable to coordinate more than on a neighborhood level in parks and by candle-light in small auditoriums.
There was collateral damage in southern Canada and northern Mexico, but the government of Mexico was mostly unaffected. Canada, with most of its population along the US border, was just as affected as their neighbors to the south.
In the USA, as in most developed countries, the government had shielded communications allowing for a short-term survival. However, by the end of 1984 existing communications had deteriorated to such an extent that the American administration had moved to Australia to maintain a semblance of control.