SEOUL, South Korea — While “CBS This Morning” co-host Norah O’Donnell and her team were in South Korea, the U.S. Army took CBS News on an aerial tour to give us a first-hand look at what they are doing to counter threats from North Korea.

We hitched a ride from Yongsan Army Garrison on a pair of Black Hawk helicopters for a bird’s-eye view of Seoul, one of the densest cities in the world that’s less than 40 miles from the North Korean border.

“When you talk about 25 million people, it just goes, I mean, to the horizon,” Eighth Army chief of staff Col. William Taylor said.

“It’s unbelievable. I mean, it’s more packed than New York City,” O’Donnell said.

Taylor said it’s all within reach of Kim Jong Un’s artillery.

“What kind of damage can long-range artillery do?” O’Donnell asked.

“A lot. It’s very destructive, you know. Very destructive,” Taylor said.

One study estimates about 2,800 people could die in an initial volley of artillery fire, and some 64,000 lives could be lost if it continued for an entire day. Maj. Gen. Tammy Smith said that’s one of the reasons the military is moving its headquarters 40 miles south to Camp Humphreys.

“We get out of the range of the long-range artillery and it removes that immediate threat,” Smith said.

At 3,400 acres, Humphreys is the largest peacetime construction project in U.S. military history with South Korea picking up over 90 percent of the bill. We landed a short distance away at Osan Air Base, home of the 35th Air Defense Artillery.

Their motto is “ready to fight tonight.” We saw soldiers preparing Patriot missiles to shoot down incoming ballistic missiles from North Korea.

“What you see here is we’re doing a PAC-3 missile reload,” said Lt. Col. Marc Pelini, commander of 6-52 Air Defense Artillery Battalion.

“How accurate is it?” O’Donnell asked.

“It’s very accurate. Very, very accurate,” Pelini said.

In the Gulf War, the Patriot missile had just a nine-percent success rate. But Pelini said it’s now a key piece of protection.