Electromagnetic Pulse - Practical Considerations For Nuclear EMP

Practical Considerations For Nuclear EMP

Older, vacuum tube (valve) based equipment is generally much less vulnerable to EMP than newer solid state equipment. Soviet Cold War–era military aircraft often had avionics based on vacuum tubes due to both limitations in Soviet solid-state capabilities and a belief that the vacuum-tube gear would survive better.

Although vacuum tubes are far more resistant to EMP than solid state devices, other components in vacuum tube circuitry can be damaged by EMP. Vacuum tube equipment was damaged in 1962 nuclear EMP testing. Also, the solid state PRC-77 VHF manpackable 2-way radio survived extensive EMP testing. The earlier PRC-25, nearly identical except for a vacuum tube final amplification stage, had been tested in EMP simulators but was not certified to remain fully functional.

Many nuclear detonations have taken place using bombs dropped by aircraft. The B-29 aircraft that delivered the nuclear weapons at Hiroshima and Nagasaki did not lose power due to damage to their electrical or electronic systems. This is simply because electrons (ejected from the air by gamma rays) are stopped quickly in normal air for bursts below roughly 10 km (about 6 miles), so they do not get a chance to be significantly deflected by the Earth's magnetic field (the deflection causes the powerful EMP seen in high altitude bursts), thus the limited use of smaller burst altitudes for widespread EMP.

If the aircraft carrying the Hiroshima and Nagasaki bombs had been within the intense nuclear radiation zone when the bombs exploded over those cities, then they would have suffered effects from the charge separation (radial) EMP. But this only occurs within the severe blast radius for detonations below about 10 km altitude.

During nuclear tests in 1962, EMP disruptions were suffered aboard KC-135 photographic aircraft flying 300 km (190 mi) from the 410 kt (1,700 TJ) Bluegill Triple Prime and 410 kt (1,700 TJ) Kingfish detonations (48 and 95 km (30 and 59 mi) burst altitude, respectively) but the vital aircraft electronics were far less sophisticated than today and the aircraft were able to land safely.