People are milling around calmly, clutching hot coffees, making small talk. Kids are chasing each other around an air hangar.

It's hard to believe they are practicing a high-stakes emergency evacuation that simulates what would happen if North Korea invaded.

"In real life, everyone would be wearing masks, rushing through places," says mom of two Nicholle Martinez. "There would be chaos everywhere. It would be scarier."

Nicholle met Nick Martinez when they were both stationed with the US military in Seoul. They've now been married for nine years and have two beautiful, energetic and charismatic children. Briannah, 6, is in first grade, and Alannah, 8, is in third.

In many respects they're very typical. They go to church on Sundays and have lunch together afterward. They like to play sports -- mom and dad want the girls to grow into healthy, strong young ladies.

Briannah wants to be a teacher, Alannah wants to be president.

But, because the whole family is now living on post in Seoul, the Martinez family lives with the ever-present danger of a very noisy and unpredictable neighbor -- Kim Jong Un.

In the face of escalating tension, the Martinez women are practicing their path to safety.

In a military-led exercise, they traveled by bus, helicopter and military plane from South Korea all the way to the Pacific island of Okinawa, Japan.

In a CNN exclusive, we went along with them for the ride.

All those taking part in the drill are volunteers -- relations of US soldiers stationed in Seoul. Unlike in a real scenario, they've had the opportunity to plan a little for this event.

Nicholle with Briannah (L) and Alannah (R). Nicholle says they feel very safe in South Korea.

However, for all the claims this is a routine practice run, Kim's threats loom over the exercise.

"He's said publicly that we're the enemy," says Sturn.

"With all the rhetoric that comes out of North Korea, of course we have to prepare for the worst case scenario."

Bags sit on the runway in South Korea. Families have to carry food and water with them as well as personal items.

Military families stationed in South Korea are encouraged to have a bag ready to go at all times. "I have a duffel bag that is always packed with sleeping bags and canned food," says Nicholle.

According to Sturn, the decision to get soldiers' families out of the country would come right from the top. A non-combatant evacuation order (NEO) is a political decision, not a military one.

"We would conduct the mission, but the execution is still a Department of State decision," says Sturn.

The Army is trying to make the environment as realistic as possible.

Family members are permitted to bring along 60 pounds of personal stuff each. Military representatives urge the group to only bring the bare essentials.

I ask the Martinez family what went into their bags first.

"My cellphone!" says Nicholle in a heartbeat.

"My blanket," says 8-year old Alannah. She wraps her comfort around herself like a cape.

Briannah pauses, shyly. Mom and sister exclaim they know exactly what went into her rucksack first.

'Daddy Doll''s face has a clear pocket where a photo of Dad can go.

The 6-year-old takes a moment to rummage in her bag and produces her must-have item with a flourish -- a military issue doll given to the girls when Nick went on his first tour.

"Daddy doll!"

The girls are carrying their must-have items, but one lesson Nicholle says she's already learned from the exercise is to pack a little lighter. Although she's a strong fitness instructor, she's weighed down with over 150 pounds of luggage and it's slowing her down.

A string of tents is pitched at Yongsan Garrison military base. There's an icy wind and a trace of nervous anticipation in the air as families slowly gather.

This is the first time since 2010 the evacuation simulation has gone all the way to Okinawa. Most people aren't really sure what to expect -- they've just been told, "it's not going to be comfortable."

The Army estimates approximately 60 people are taking part in the military exercise.

The group are issued with identity bracelets that will track their progress from South Korea to Okinawa. If this were a genuine evacuation, the families would then be flown back to the United States from Japan.

There is a security screening and the opportunity to register any pets traveling. The Martinez family joke that the fish didn't make the cut.

One stage of the registration process also includes instructions on the ICAPS mask -- or Infant Chemical Agent Protective System -- that protects against the effects of biological attacks for up to 12 hours.

Parents are shown how to administer the ICAPS after they enable their own protection.

There's a lot of nervous laughter and "Ghostbusters" references abound. Briannah gets into the spirit of things.

But for all the smiles and calm instruction, the vision of a 6 year-old preparing for a chemical or biological attack isn't a comfortable one.

Nicholle, who herself was in the military police, says that as well as being a great life experience, it's a good opportunity for the girls to get some insight into what dad does for a living. "They only have five more years until dad retires," she says. "So being here has opened their eyes as to what military life is."

Alannah is already showing signs of logistical aptitude. She tells me she's not sure why they'd take so many steps to evacuate the country, if it really was an emergency.

I suggest it might seem easier just to get families onto a commercial flight in Seoul.

"That's what I would do!" she says. "Just get outta there."

I put Alannah's question to Sturn, who says the movement south would be in response to hostile maneuverings from the north and the "need to move people out of that hotspot."

"If it was a natural disaster, or something like that, we would absolutely fly them out of Seoul," says Sturn.

"But this is the worst-case scenario. And the worst-case scenario is North Korea is coming across the border, and we need to get people out of harm's way."

After about an hour's drive in convoy from the registration point in Seoul, we arrive at Camp Humphreys, further south in Pyeongtaek.

We're taken through a hangar full of military hardware towards two US Army CH-47s, or Chinook helicopters, sitting on the tarmac.

We're given a safety orientation, issued earplugs and escorted on to the machine.

This is the first time most of the civilians have flown in a military helicopter. The roar, heat and pure force from the blades is overwhelming as we get on board.

If they had to evacuate by helicopter, this is a fair enactment of how it would go, says Col. Lance Calvert, commander of the 2nd Combat Aviation Brigade. However, with the increased numbers a real-life scenario would entail, he says there would be more practical ways to transport people out of Pyeongtaek.

It's estimated that -- if this were a genuine evacuation of non-combatants from South Korea -- the order could be for tens of thousands of civilians to leave over a period of five to seven days. "Trains, buses or commercial transportation systems are much more efficient," he says.

The aim of the drill isn't only to try to give relatives a realistic practice run. The military also considers the "mental aptitude" of a soldier in a crisis and believes exercising this process builds confidence. It shows acting service members that, in a dangerous situation, their family members would be cared for.

"In a natural disaster or hostile scenario, the last thing you want is your soldier thinking about his family,'" says Capt. Jimmy Sheehan.

Capt. Sheehan: "'You don't want your soldier thinking: 'Where's my wife, where's my husband?'"

The helicopters land in Daegu. After a mess dinner, we spend a chilly night in the dormitories on the US military base, Camp Walker. The next morning, we're up at 5 a.m.

Despite the intensity and length of the journey so far, all the kids in the group are still in good spirits. A trip to Okinawa aquarium is nearly within grasp.

A convoy through the spectacular mountainous south takes us to Gimhae Republic of Korea Air Force (ROKAF) base where we're escorted on to a US Air Force C-130 Hercules transport plane for the drill's final leg -- onwards to Japan.

The Hercules is an impressive beast, and the "non-combatants" run into it in anticipation of arriving in warmer southern climes.

Earplugs at the ready, we're strapped in. Most of the children curl up and nod off -- an oddly peaceful scene in such a stark environment.

When they arrive in Okinawa family members have a night in a military gym to look forward to.

Landing in Japan is the highlight for the Martinez girls, who tell me with great enthusiasm how much they like exploring new places.

"For some reason, I thought we were going to go on a secret subway tunnel!" says Alannah. Her younger sister interjects wistfully: "I wish we could go through a tunnel to a magical place."

"Just close your eyes and imagine it," laughs mom.

She says they seize these kinds of opportunities because, as a military family that's often on the move, they try to make the best of it everywhere they go.

Nicholle Martinez: "We struggle at the beginning... It's just an adjustment, but once you get used to it, you love it here."

"You adapt and you will succeed, or you will be miserable if you don't," she says. "We embrace these kinds of events because we help our spouses. My husband benefits from us enjoying our time here. If we're happy, he's happy."

For Nicholle, the experience has also made her reflect on how an emergency evacuation would really feel. The idea of leaving all the material things behind isn't difficult.

"The most important thing is that I get my girls to a safe place,"' she says.

But it has driven home what, for her, would be the most painful part of the process.

"Knowing that I would be leaving my husband behind... that would be the hardest thing."