If the United States were to strike North Korea, Kim Jong Un’s regime would retaliate by unleashing its conventional weaponry lined up on the demilitarized zone that has separated the two Koreas for about seven decades. 

And that conventional weaponry is reliable, unlike North Korea’s missiles, and could cause major devastation in South Korea, which is a staunch ally of the United States.  

“This becomes a very limiting factor for the U.S.,” said Carl Baker, a retired Air Force officer with extensive experience in South Korea.

As tensions between North Korea and the outside world have risen over the past month, there has been increasing talk about the United States using military force either to preempt a North Korean provocation or to respond to one. 

That talk continues even after it emerged that the Navy had not sent an aircraft carrier strike group to the Korean Peninsula region, as officials, including President Trump, had implied. 

Sen. Lindsey O. Graham (R-S.C.) said this week that he supported striking North Korea to stop it from developing the capability to reach the United States with a missile — even if that came at a huge cost for the region.

“It would be terrible, but the war would be over [in South Korea], it wouldn’t be here,” Graham said in an interview with NBC.

Although most of the recent focus has been on North Korea’s ambition to be able to strike the continental United States with a missile, the people of South Korea have been living under the constant threat of a conventional North Korean attack for decades. 

North Korea has “a tremendous amount of artillery” right opposite Seoul, said Joseph S. Bermudez Jr., a senior imagery analyst at 38 North, a website focused on North Korea. 

The Second Corps of the Korean People’s Army stationed at Kaesong on the northern side of the DMZ has about 500 artillery pieces, Bermudez said. And this is just one army corps; similar corps are on either side of it.

All the artillery pieces in the Second Corps can reach the northern outskirts of Seoul, just 30 miles from the DMZ, but the largest projectiles could fly to the south of the capital. About 25 million people — or half of the South Korean population — live in the greater Seoul metropolitan area. 

(Bastien Inzaurralde/The Washington Post)

“It’s the tyranny of proximity,” said David Maxwell, who served in South Korea during his 30 years in the Army and now teaches at Georgetown University. “It’s like the distance between Baltimore and Washington, D.C. Imagine a million-man army just outside the Beltway with artillery they could use to terrorize Washington.”  

About half of North Korea’s artillery pieces are multiple rocket launchers, including 18 to 36 of the huge 300mm launchers that Pyongyang has bragged about. State media last year published photos of the system during a test firing that Kim attended. 

The 300mm guns could probably fire eight rounds every 15 minutes, Bermudez said, and have a range of about 44 miles.

“This could do a lot of damage,” he said. “If they hit a high-rise building with a couple of rounds of artillery, people get into their cars, causing huge traffic jams, so North Korea could target highways and bridges in cascades.” 

If North Korea were to start unleashing its artillery on the South, it would be able to fire about 4,000 rounds an hour, Roger Cavazos of the Nautilus Institute estimated in a 2012 study. There would be 2,811 fatalities in the initial volley and 64,000 people could be killed that first day, the majority of them in the first three hours, he wrote. 

Some of the victims would be American, because the U.S. military has about 28,000 troops in South Korea. The higher estimates for the 300mm rocket launcher’s range — up to 65 miles — would put the U.S. Air Force base at Osan and the new military garrison at Pyeongtaek, the replacement for the huge base in Seoul, within reach. 

This prospect of extensive damage and casualties has restrained successive U.S. administrations, however provocative North Korea has been. 

“Every U.S. administration, as they have looked at this problem, has said that all options are available. But that’s not really true,” said Baker, who is at the Pacific Forum of the Center for Strategic and International Studies. “We really don’t have a military option.” 

Vice President Pence, speaking in Seoul this week, said that all options are on the table for dealing with North Korea, echoing statements that Secretary of State Rex Tillerson made in Seoul last month. 

There was a similar discussion in 1994, when North Korea threatened to go nuclear, sparking talk of surgical strikes.

“People in Washington were saying, ‘We have the capability to do this,’ but those of us who were sitting in Seoul said, ‘You can’t do that,’ ” Baker said.

It is not just South Korea that would suffer. Such action would be devastating for North Korea, too, because the U.S. and South Korean militaries have spent decades developing their counter-battery capability, as well as developing plans for airstrikes to take out North Korea’s facilities.

“Defending Seoul against such a threat is the top priority for the alliance,” said Chun In-bum, a retired lieutenant general in the South Korean army who served as commander of South Korea’s Special Warfare Command.

“The U.S. and South Korean response would be immediate. We have assets along the DMZ dedicated for doing this job and counter-battery units trained to conduct these missions,” Chun said.

Although the White House has doubled down on its statements on the USS Carl Vinson heading to the Korean Peninsula — “It’s happening,” spokesman Sean Spicer said this week — former military officers on both sides of the alliance say they are sure that Trump will not put South Korean lives at risk.

“I believe that General [Jim] Mattis and General [H.R.] McMaster are well aware of this,” Maxwell said, referring to the defense secretary and the national security adviser. 

“Of course it concerns me,” Chun said of the recent talk about strikes, “but I’ve always believed that, with good common sense and engagement, cooler heads will prevail.”