On Sunday, North Korea launched a missile into the Sea of Japan for the first time since US President Donald Trump took office.
South Korean officials told Reuters the missile, a land-based adaptation of the submarine-launched KN-11, doesn't have the range to strike the US but has another trait that's just as troubling, if not more — solid fuel.
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North Korean missiles usually rely on liquid fuel and have to be gassed up like you'd fill up your car.
North Korea, like many nuclear powers, mount their nuclear-capable missiles to trucks.
Road-mobile missile launchers can hide easier, launch from almost anywhere, and take an enemy by surprise — but liquid fuel complicates all that.
To launch a liquid-fueled missile, a giant convoy of military trucks must drive out to a location, fuel up the rocket with the multiple types of fuel for the different stages of launch, and then fire away. This requires dozens of trucks and associated military personnel. Such a large-scale deployment is much harder to conceal from a vigilant foe.
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"Liquid-fueled missiles are more vulnerable to tracking and preemptive strikes. Solid-fueled ballistic missiles are not fueled on site and therefore pose more of a threat because solid-fueled ballistic missiles require less support and can be deployed more quickly," Kelsey Davenport, the director of nonproliferation policy and a North Korea expert at the Arms Control Association, told Business Insider.
Using a missile like the one tested on Sunday, North Korea could simply park a truck and let a missile fly.
"Another striking feature of the test was the transport erector launcher that was used to launch the missile. Images indicate that it ran on treads rather than wheels," said Davenport. "This allows North Korea to move its missiles through more difficult terrains."
To counter such a sneaky launcher, an adversary would have to spend extensively on surveillance and recon technology.
So while North Korea remains without an ICBM to directly threaten the US homeland, their successful launch of a solid-fueled missile means they have developed a very destabilizing technology that can strike US military bases, South Korea, or Japan in a moment's notice.
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