TOKYO -- North Korea again launched a ballistic missile in the morning of April 29, amid growing tensions over its weapons program and increasingly threatening rhetoric between Pyongyang and Washington.
Since the missile exploded in mid-flight, many experts branded the test a failure.
But it could also have been a thinly-disguised warning. Pyongyang could have been saying, "We could launch an electromagnetic pulse (EMP) attack if things get really ugly." A powerful EMP would cause catastrophic damage to electrical grids and communications networks in surrounding nations, creating chaos.
An EMP attack is based on a phenomenon the U.S. and the Soviet Union discovered and studied during their atmospheric tests of nuclear weapons in the Cold War era.
A nuclear explosion generates a strong EMP. To maximize the damaging effect of an EMP resulting from a nuclear explosion, the bomb must be detonated at a high altitude where the air is thin.
The strong EMP produced by a high-altitude nuclear explosion instantly generates powerful electric currents in antennas and electric cables on the ground, which in turn lead to overcurrent and overvoltage in electric devices, causing them to break down or malfunction.
The North Korean missile launched on April 29 exploded at an altitude of 71km, according to the South Korean military. It was within the ionosphere, the ionized layer of the Earth's atmosphere, where a nuclear blast can generate enormously destructive effects.
Hard to predict
The equipment and facilities of the U.S. military are protected from the impact of an EMP with protective shields and other measures. But power grids and other general infrastructure are not.
An EMP attack could cause serious, long-term disruptions in the society in Japan, South Korea, northeastern China and Russian Far East. It could shut down power grids and computer systems. The consequences would be long-term nationwide power outages and prolonged disruptions in water and gas supplies, as well as in broadcasting and telecommunications.
The J-Alert nationwide warning system would fail to work, and the public would be deprived of access to TV, radio and internet.
The financial system and factory production could also grind to a halt.
In short, a single high-altitude nuclear blast could be used to disable an entire country.
A 1962 high-altitude nuclear test above the Pacific Ocean conducted by the U.S. created an EMP that was so powerful it caused a power outage in Hawaii.
The consequences of a HANE would be far more disastrous today because of widespread use of sophisticated electronics and society's heavy dependence on such devices. But it is impossible to assess accurately the actual scale of damage from an EMP attack.
The use of a weapon whose effects are unknown is considered taboo in the military world.
North Korea's military actions are often intended as messages that only military experts can decode.
When North Korea fired seven ballistic missiles into the Sea of Japan in 2006, for instance, the message was that if a U.S. carrier strike group came close to the country it could drop a nuclear bomb over the vessels to destroy them all.
When Pyongyang launched four missiles in March this year, it was an implied threat to stage a saturation attack against U.S. military bases in Japan to overwhelm the missile defense system.
When North Korea conducted a massive live-fire artillery drill on April 25, it was apparently a threat to rain shells on Seoul if the U.S. makes a surprise attack on Pyongyang.
This time, it seems that the secluded and unpredictable regime of North Korean leader Kim Jong Un, alarmed by a U.S. carrier strike group's move into the Sea of Japan, signaled its willingness to resort to an EMP attack.
The question now is how the U.S. administration of President Donald Trump will respond to this latest provocation by North Korea.
A group of retired generals handpicked by Trump to fill top administration positions, including Defense Secretary James Mattis and National Security Adviser H.R. McMaster, have gained significant influence over the administration's security policy.
Top military officers who know well the harsh reality of the battlefield are generally cautious about starting wars. But they also abhor backing down in the face of intimidation by an enemy.
The U.S. military has defeated the regimes of such dictators as Saddam Hussein of Iraq and Moammar Gadhafi of Libya.
Its pride will not allow it to give in to intimidation by the young North Korean dictator.
In the previous administration of President Barack Obama, civilian officials had enough control over the country's security policy to rein in the military.
But it is unclear whether civilian control will work in the same way within the Trump administration, in which former generals play a key role in the policymaking process.
North Korean leader Kim Jong Un is behaving like a knife-brandishing fanatic who has holed up in a place threatening to attack any person who approaches him.
If he threatens to use an EMP weapon, its potential destructive power could prod the U.S. military into drastic action.
On April 29, Pope Francis expressed concerns about rising tensions between the U.S. and North Korea, saying the situation "has heated up too much."
The Vatican has a powerful global information-gathering network. Since the Pope, as the head of the Holy See, has access to all this information, there is good reason to pay close attention to what he says about the dangerous and volatile situation.
Japan should prepare for various possible developments without ignoring the possibility of the situation worsening even more.
The Japanese government is now scrambling to work out plans to protect the nation from the possible consequences of military conflict on the Korean Peninsula, including a plan for evacuating people during a missile attack.
Some people have criticized or derided the government's actions. But this is clearly time for all of Japan to act swiftly to prepare itself for a security emergency.