News of North Korea’s latest nuclear development, which appears to be a hydrogen bomb estimated to be five to ten times more powerful than any previous nuclear ordnance North Korea possessed, has sent shockwaves around the world.  No longer does Kim merely possess the destructive power of an atom bomb, he now has a thermonuclear city killer – but in all sincerity, that may be the least of our worries.

One of the byproducts of a nuclear reaction is the release of a powerful electromagnetic pulse.  That pulse overloads the circuits inside non-hardened electronic devices, knocking out the power and often damaging those circuits beyond repair.  Of course, the subsequent power outage often goes unnoticed, as the residents of a targeted city try to dig themselves out from the irradiated rubble that was once their homes… but what if a thermonuclear weapon were to detonate high in the atmosphere above us?  Well, then we’re going to notice.

If Kim were to choose to attack the United States, an EMP-based attack would likely be the better option, over a direct nuclear strike.  Concerns about the survival of North Korea’s re-entry vehicles could be mitigated by detonating higher in the atmosphere, and while one thermonuclear warhead could feasibly wipe out the majority of a city, the same warhead could also potentially cripple a far larger swath of the nation.  Kim seems to be well aware of this, as North Korea’s announcement of a successful hydrogen bomb test came coupled with threats of an EMP attack.

So how exactly would such an attack unfold?  It would invariably start with the launch of one of North Korea’s long range ballistic missiles, likely their most successful platform to date, the Hwasong-14 (which goes by the U.S. designation KN-20).  In fact, in order to successfully pull off this attack, North Korea would need to launch a volley of such missiles, as a large percentage of them would likely be intercepted long before they could reach the skies above the U.S.

THAAD emplacements in South Korea would immediately identify the launch and begin calculating a trajectory, as would Aegis missile defense platforms aboard both U.S. and Japanese naval vessels.  Depending on the trajectory employed by the ICBMs, THAAD launchers in Kodiak, Alaska could also be called on to engage these missiles as they sailed high over the Pacific.  In all likelihood, a North Korean ICBM attack on the mainland United States would end there, as interceptors ranging from kinetic impactors launched by the THAAD to traditional SM-6s launched by ships could be employed in the intercept effort.

However, if one or more long-range, thermonuclear tipped missiles were to slip through the two layers of protection provided by THAAD and Aegis systems, the missiles would still have to get past America’s troubled, but competent, Ground-based Midcourse Defense system, or GMD.  Because the GMD’s track record is spotty, the United States would likely launch as many as five interceptors at each inbound ICBM, ensuring at least one of them would successfully destroy the missile somewhere along its flight path.  This strategy would prove effective, unless North Korea somehow managed to field enough missiles to overwhelm all three layers of missile protection.

Unlikely as it may seem that a North Korean missile could get past each of these advanced defensive systems, a number of variables could improve their chances.  Launching a huge number of missiles at once, aimed at targets locally as well as the mainland, could suffice to overwhelm the equipment, or personnel, tasked with manning the THAAD and Aegis systems, leaving only the GMD to hopefully accomplish the intercept.  Unforeseen circumstances could also improve their chances at victory, as depicted in the recent dogfight between a Navy F/A-18 Super Hornet and a comparably outmatched Syrian SU-22 in the skies over Syria.  The Super Hornet first fired the most advanced air-to-air missile platform we have, the AIM-9X Sidewinder, at the SU-22 and missed.  The old jet’s flares were outdated and dirty, which allowed them to successfully fool the missile designed to outsmart the flare systems employed by the latest in enemy fighters.  In short, American gear may prove less effective against North Korean missiles than against our own test-platforms, and there’s really no way to know until we attempt to engage one.

Thus far, everything about this method of attack mirrors a traditional nuclear strike in every way, but the real difference comes from re-entry.  Instead of the missile needing to make it all the way to a surface city (or slightly above the surface), it would only need to detonate above the atmosphere.  The result would be an immediate, and mostly permanent, power loss for as much as 75% of the entire nation.