Here's how a preemptive strike on North Korea would go down

US President Donald Trump has apparently identified North Korea as his most serious external challenge, and he has reportedly declared the country the single greatest threat to the US. On Friday, Trump tweeted: "North Korea is behaving very badly. They have been 'playing' the United States for years." He also blamed China, the North's biggest ally, for not doing more to help.

In reality, taking out North Korea's nuclear capabilities, or toppling the Kim regime, would pose serious risks to even the US military's best platforms.

Business Insider spoke with Stratfor's Sim Tack, a senior analyst who is an expert on North Korea, to determine exactly how the US could carry out a crippling strike against the Hermit Kingdom.

First, a decision would need to be made.

Military action against North Korea wouldn't be pretty. Civilians in South Korea, and possibly Japan, and US forces stationed in the Pacific would be likely to die in the undertaking no matter how smoothly things went.

In short, it's not a decision any US commander in chief would make lightly.

But the US would have to choose between a full-scale destruction of North Korea's nuclear facilities and ground forces or a quicker attack on only the most important nuclear facilities. The second option would focus more on crippling North Korea's nuclear program and destroying key threats to the US and its allies.

Since a full-scale attack could lead to "mission creep that could pull the US into a longterm conflict in East Asia," according to Tack of Stratfor, the US would most likely focus on a quick, surgical strike that would wipe out the bulk of North Korea's nuclear forces.

Then, the opening salvo: A stealth air blitz and cruise missiles rock North Korea's nuclear facilities.

The best tools the US could use against North Korea would be stealth aircraft like the F-22 and the B-2 bomber, Tack said.

The US would gradually position submarines, Navy ships, and stealth aircraft at bases near North Korea in ways that avoid provoking the Hermit Kingdom's suspicions.

Then, when the time is right, bombers would rip across the sky and ships would let loose with an awesome volley of firepower. The US already has considerable combat capability amassed in the region.

"Suddenly you'd read on the news that the US has conducted these airstrikes," Tack said.

While the F-22 and the F-35 would certainly operate over North Korean missile-production sites, it really is a job for the B-2.

As a long-range stealth bomber with a huge ordnance capacity, the B-2 could drop 30,000-pound bombs on deep underground bunkers in North Korea — and it could do it from as far away as Guam or the continental US.

The first targets ...

The initial targets would include nuclear reactors, missile-production facilities, and launching pads for intercontinental ballistic missiles, Tack said.

Cruise missiles would pour in from the sea, F-22s would target North Korea's rudimentary air defenses, and B-2s would pound every known missile site.

Planes like the F-35 and the F-22 would frantically hunt down mobile missile launchers, which can hide all over North Korea's mountainous terrain. In the event that North Korea does get off a missile, the US and South Korea have layered missile defenses that would attempt to shoot it out of the sky.

Next, the US would try to limit North Korean retaliation.

Once the US has committed the initial strike against North Korea, how does Kim Jong Un respond?

Even with its nuclear facilities in ashes and most of its command and control destroyed, "North Korea has a lot of options," Tack said. "They have their massive, massive conventional artillery options that can start firing at South Korea in a split second."

But as the graphic below shows, most North Korean artillery can't reach Seoul, the South Korean capital.

Additionally, Seoul has significant underground bunkers and infrastructure to quickly shield its citizens, though some measure of damage to the city would be unavoidable.

According to Tack, much of this artillery would instead fire on the demilitarized zone between the two Koreas, detonating mines so North Korean ground forces could push through. Also within range would be US forces near the DMZ.

Some 25,000 American troops are stationed in South Korea, and they would face grave danger from North Korea's vast artillery installations.

But the North Korean artillery isn't top of the line. It could focus on slamming US forces, or it could focus on hitting Seoul, but splitting fire between the two targets would limit the impact of its longer-range systems.

Additionally, as the artillery starts to fire, it becomes an exposed target for US aircraft.

The next phase of the battle would be underwater.

North Korea has a submarine that can launch nuclear ballistic missiles, which would represent a big risk to US forces as it can sail outside the range of established missile defenses.

Fortunately for the US, the best submarine hunters in the world sail with the US Navy.

Helicopters would drop special listening buoys, destroyers would use their advanced radars, and US subs would listen for anything unusual in the deep. North Korea's antique submarine would hardly be a match for the combined efforts of the US, South Korea, and Japan.

While the submarine would greatly complicate the operation, it would most likely find itself at the bottom of the ocean before it could do any meaningful damage.

What happens if Kim Jong Un is killed?

"Decapitation," or the removal of the Kim regime, would be a huge blow to the fiercely autocratic Hermit Kingdom.

Reports have indicated Kim Jong Un has engaged in a vicious campaign to execute senior officials with packs of dogs, mortar fire, and antiaircraft guns for a simple reason, according to Tack: They have ties to China.

Kim's removal of anyone senior with ties to China means he has consolidated power within his country to a degree that makes him necessary to the country's functioning.

Without a leader, North Korean forces would face a severe blow to their morale as well as their command structure, but it wouldn't end the fight.

"Technically North Korea is under the rule of their 'forever leader' Kim Il Sung," Tack said, adding that "a decapitation strike wouldn't guarantee that the structures below him wouldn't fall apart, but it would be a damn tricky problem for those that remain after him."

North Koreans aren't shy about putting their leader first, however, and at the first indication of an attack, Kim would most likely be tucked away in a bunker deep underground during the attack.

Then the US defends.

"If North Korea doesn't retaliate, they've lost capability and look weak," Tack said.

Indeed, few would expect North Korea to go quietly after suffering even a crippling attack.

Through massive tunnels bored under the DMZ, North Korea would try to pour ground troops into the South.

"The ground-warfare element is a big part of this," Tack said. "I think that the most likely way that would play out would be the fight in the DMZ area," where the US would not try to invade North Korea but rather would defend its position in the South.

Though North Korea's air force is small and outdated, it jets would need to be a target of the US and allied forces.

Meanwhile ...

US special operations forces, after North Korea's air defenses have been destroyed, would parachute in with the goal of destroying or deactivating mobile launchers and other offensive equipment.

The US would face a big challenge in trying to hunt down some 200 missile launchers throughout North Korea, some of which have treads to enter very difficult terrain where US recon planes would struggle to spot them.

It would be the work of US special forces to establish themselves at key logistical junctures, observe the North Koreans' movements, and then relay that to US air assets.

So how does this all end?

North Korea is neither a house of cards nor an impenetrable fortress.

Additionally, the resolve of the North Koreans remains a mystery. North Korea successfully estimated that the international community would be unwilling to intervene as it quietly became a nuclear power, but that calculation could become its undoing.

North Korea would most likely launch cyberattacks, possibly shutting down parts of the US or allies' power grids, but US Cyber Command would prepare for that.

North Korea would most likely destroy some US military installations, lay waste to some small portion of Seoul, and get a handful of missiles fired — but again, US and allied planners would stand ready for that.

In the end, it would be a brutal, bloody conflict, but Tack said even the propaganda-saturated North Koreans must be aware of their disadvantages.

Even after a devastating missile attack, some of North Korea's nuclear stockpile would most likely remain hidden. Some element of the remaining North Korean forces could stage a retaliation, but what would be the point?

"If they chose to go the route of conducting a large-scale retaliation, they're inviting a continuation of the conflict that eventually they cannot win ... Nobody in this whole game is going to believe that North Korea can win a war against the US, South Korea, and Japan," Tack concluded.