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.

Bird's-eye view of Seoul, South Korea CBS News





"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.

Col. William Taylor with Norah O'Donnell CBS News

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.

U.S. soldiers preparing Patriot missiles to shoot down incoming ballistic missiles from North Korea. CBS News

"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.



"We're truly the first line of defense," Pelini said. "We buy decision space for the president and for the CFC Cmdr. Gen. [Vincent] Brooks make decisions on how to potentially deescalate or escalate the conflict as necessary."

In the face of international condemnation, North Korea has conducted 10 missile tests this year. Two of them involved solid-fuel missiles, which the North can launch with less warning.



"Why do these solid fuel rockets make it harder?" O'Donnell asked.

"Because it doesn't require as much preparation for them to take a missile and prepare it and get it ready for launch," said Col. Rick Wright, commander of the 35th Air Defense Artillery Brigade.

Wright took us inside an "engagement control station" where the pressure would be on to shoot down any incoming threat.



"So this is where they'd would essentially push the button to launch it," O'Donnell said.

"Absolutely. This is where the tactical control officer and his assistant would actually execute the air battle," Wright said.

"We routinely exercise that… From the phone call that would come into me, to actually moving them on the road, to potentially putting a missile up in the air," Pelini said.

"How quickly can you do that?" O'Donnell asked.

"I can do it pretty fast," Pelini said, adding, "We practice it very routinely."