The Trump administration sees no good military options in North Korea.



The rogue regime’s missile tests are growing more frequent, and Kim Jong Un is closer than ever to being able to deliver a nuclear-tipped missile to the United States’ West Coast.



Yet given Seoul’s proximity to the border, military leaders fear that any preemptive strike would almost certainly set in motion a cataclysmic chain of events resulting in profound loss of life.



Recently, the military has taken a back seat to the State Department, where U.S. officials continue to push diplomatic and economic measures, hopeful, with the help of China, it can pressure the regime to halt its provocations voluntarily.



But if diplomatic efforts fail and a conventional war ensued with all but nuclear weapons being deployed, experts agree that the scenario would involve massive amounts of U.S. and South Korean forces in the first days — and possibly drag on for many months or longer.



In a Friday press conference, when asked by reporters about the current tensions with North Korea, Secretary of Defense Jim Mattis said, "If this goes to a military solution, it’s going to be tragic on an unbelievable scale."



Military Times has constructed a detailed picture of what war on the Korean Peninsula might look like, based on numerous interviews with current and former military officials, international experts and intelligence assessments of the North Korean military’s capabilities.



"Anybody that assumes this could be knocked out in 30 days would be dead wrong," said retired Army Lt. Gen. Mark Hertling. "There would be literally thousands, tens of thousands, some say more than 100,000 civilian casualties."



What follows is a matter-of-fact look at the full-blown conventional war that would be unleashed if artillery rounds began to arc over the 38th parallel, ending the tense 64-year-old ceasefire on the peninsula.



Day one



U.S. and South Korean forces would respond instantaneously with the help of the American Army, Air Force, Marines and Navy.



The tip of the spear would be the U.S. 8th Army pushing the 2nd Infantry Division — a combined division of American and South Korean troops — into the fight, bringing with it a combat aviation brigade, a field artillery brigade, an armored brigade combat team, and a chemical weapons battalion.



Throngs of U.S. aircraft would streak across the skies over the peninsula in a narrow battlespace, fighting a multi-nation war in an area the size of Minnesota.



Using sophisticated air defense, anti-artillery systems and air power, they hit key North Korean military positions.



Plans call for the South Korean military, with more than 650,000 active personnel and another 3 million in reserve, to do most of the initial fighting.



There are about 30,000 U.S. troops in South Korea.



Smoke rings launched by a South Korean army K200 Infantry Fighting Vehicle burst over a training ground where South Korean and American troops practiced working as a single force to assault an objective. Photo Credit: Sgt. Christopher Dennis/Army

In the opening hours, U.S. officials alert Marines on Okinawa to begin loading gear onto ships to head toward the fight, while back in the United States the call goes out to the Army’s 82nd Airborne Division to prepare its brigade combat team of paratroopers that’s part of America’s Global Response Force, poised to deploy within hours when needed.



The U.S. Navy would annihilate the North Korean navy, said Jerry Hendrix, a retired Navy captain and analyst with the Center for a New American Security.



"At the outset we will find every North Korean ship at sea and destroy it, or [if] in port, we’ll hit it, probably with Tomahawks," Hendrix said.



Experts predict heavy initial casualties among both U.S. and South Korean personnel.



North Korea is believed to have dug several tunnels under the Demilitarized Zone, which could allow it to rapidly deploy troops behind the minefields that separate the two Koreas, said Joost Oliemans and Stijn Mitzer, two analysts in the Netherlands who specialize on the North Korean military.



"The first tunnel discovered by the South was estimated to have allowed for the deployment of 20,000 troops per hour," they said.



A key challenge will be finding the North Korean artillery, which are hidden inside carved-out positions built with rails that allow enemy soldiers to slide the piece out of its hiding place, fire, and then pull it back into the mountainside in minutes.



"If you’re going to build hardened artillery sites, those south-facing granite mountains are just perfect," said retired Army Maj. Gen. Robert Scales.



The jagged mountains and deep valleys make the battlefield terrain a daunting challenge for land warfare.



Hertling recalled a tour he did decades ago on the peninsula, taking helicopter rides to different locations and seeing the land below for the first time.



"I just went, ‘Holy shit, this would be tough,’" Hertling said.



But air assets will give the coalition a key advantage in overcoming terrain challenges.



"If we can see their movement, we can detect it. If we can detect it, we can target it. If we can target it, we can kill it," said retired Army Special Forces Col. David Maxwell, associate director at the Center for Security Studies at Georgetown University.



North Korean strategy



North Korea’s goal would be to occupy as much of the peninsula as possible before the U.S. could send reinforcements, Maxwell said.



Rather than trying to capture Seoul, South Korea’s capital, North Korean forces would likely seek to isolate and bypass it so that the invasion doesn’t slow down, Maxwell said.



"They need speed. They need momentum," Maxwell said. "Once they get across the Han River, then they can maneuver through the rest of peninsula all the way to Pusan."



A full-scale, conventional war against North Korea would devastate the Korean Peninsula. Military experts predict North Korean forces will pour into the South quickly in a bid to maintain their momentum and choke off the South Korean capital of Seoul. Meanwhile, U.S. forces, fighting alongside their South Korean partners on land, in the air and from the sea, are expected to mobilize in full force to fend off against the North’s soldiers and artillery. Photo Credit: John Bretschneider/Staff

Meanwhile, North Korean naval infantry and special operations forces would likely launch amphibious landings east of the Taebaek Mountains along the peninsula’s east coast, he said.



The North Korean military is likely to target U.S. and South Korean air bases on the first day of the invasion, possibly with chemical weapons, Maxwell said.



A 2009 International Crisis Group cited estimates that North Korea has between 2,500 and 5,000 tons chemical weapons, including VX nerve agent.



"I think their initial targets for use of chemicals would be air bases to try to contaminate those air bases to prevent use by [Republic of Korea] and U.S. aircraft," Maxwell said.



However, chemical agents are much less effective when delivered by Scud missiles, so any contamination would be temporary, he said.



The U.S. and South Korea could rely on air bases in Japan to continue its round-the-clock campaign.



The Navy ships based in Japan — destroyers and cruisers — are equipped with sophisticated radars and software designed to shoot down ballistic missiles that the Kim regime could use to target U.S. forces in the region, as well as allies.



The Air Force’s intelligence, surveillance and reconnaissance capabilities will play a key role in allowing U.S. and South Korean forces to act fast, said retired Air Force Gen. Herbert "Hawk" Carlisle, former head of Air Combat Command.



A swarm of aircraft throughout the Pacific and beyond will converge on the airspace. The "unblinking eye" of ISR will use every asset available — cyber, intelligence, surveillance and reconnaissance, to include satellites, drones, and manned airborne warning and control aircraft such as the E-3 AWACS.



Carlisle said coalition forces would defeat the North Korean military. The only question — and the greatest danger — is whether allied forces would be able to subdue the North’s military quickly enough to reduce civilian casualties in South Korea.



"The key to minimizing the potential loss of life in South Korea is indications and warning," he said. "It’s just, how much damage can [North Korean dictator Kim Jong Un] do before we take him out?"



An Air Force security forces airman stands guard next to an F-22 Raptor after it conducted a flyover in the vicinity of Osan Air Base, South Korea, in response to provocative action by North Korea last year. The F-22 was joined by three other Raptors, four F-15 Slam Eagles and four U.S. Air Force F-16 Fighting Falcons. Photo Credit: Tech. Sgt. Travis Edwards/Air Force

'Megacity combat'



Seoul is about 35 miles from the demilitarized zone separating the two nations, and North Korean rockets and artillery could cause significant damage to the densely-populated area of about 25 million people.



Seoul is nearly twice the size of Baghdad, with significant urban sprawl. The South Korean capital city has skyscrapers such as the 123-story Lotte World Tower, which opened last month and is the fifth tallest building in the world.



North Korea’s Koksan 170 mm self-propelled guns and 240 mm and 300 mm multiple-launch rocket systems could reach Seoul from their positions, according to a May 2016 report by geopolitical analysis firm Stratfor.



Those weapons represent a small part of the North’s artillery, Stratfor said. At best, most guns could hit the northern outskirts of Seoul — and its longer-range guns have greater problems with accuracy.



"If every one of Pyongyang’s 300 mm multiple rocket launcher systems were directed against Seoul, their range would be sufficient to rain fire across the city and beyond," the report said.



A single volley would unleash 350 metric tons of explosives — roughly equivalent to ordnance dropped by 11 B-52 bombers. The world would see civilian casualty numbers equal to the entire Syrian conflict in a matter of days, Hertling said.



That creates a massive humanitarian crisis in which millions of civilians fleeing Seoul southward would clog up rail lines, air traffic and roads just as U.S. and coalition forces were pushing north, he said.



While many analysts agree that the North Koreans would push as fast as possible to gain ground in the South, one fear is the North Korean military getting significant troops into Seoul.



That could spark what Army Chief of Staff Gen. Mark Milley has referred to as the dreaded "megacity combat."



It’s a scenario that the U.S. military has not faced in a long time, if ever.



The Air Force’s ability to provide close-air support and other air power would be exceptionally limited in a megacity fight, Carlisle said.



"If [North Korea] got into some portion of Seoul, that would be incredibly difficult," Carlisle said.



The long slog



If North Korean forces gain ground, the fight would require amphibious assaults, which the U.S. Marine Corps has not done in wartime since the last Korean conflict.



The war also could last a long time and begin to drain the U.S. military’s readiness worldwide, officials say.



This image shows leader Kim Jong Un at what was said to be a missile test site at an undisclosed location in North Korea. The North Koreans on May 15 boasted of a successful launch of a new type of "medium long-range" ballistic rocket that can carry a heavy nuclear warhead. Photo Credit: KRT via AP Video

Every available U.S. aircraft carrier would likely surge into the conflict and find themselves at the center of the fight because North Korean missiles are likely to target U.S. land aircraft bases in the region, said Dan Goure, an analyst with the Lexington Institute, a think tank based in Arlington, Virginia.



Stopping the North Korean attack could involve the Marines based on Okinawa, along with South Korea’s 30,000 marines, launching amphibious landings on South Korea’s east and west coasts, Maxwell said.



"There are multiple places where they could land forces," he said. "Of course, the challenge is having enough amphibious ships to be able to land forces in sufficient strength to establish a beachhead and then conduct maneuver from the sea."



Of the roughly 84,000 Marines and sailors who make up U.S. Marine Corps Forces, Pacific, about 25,000 are based on Okinawa as part of III Marine Expeditionary Force. Okinawa and mainland Japan would serve as the jumping off point for any amphibious operations in Korea.



The Marine Corps believes that launching a successful amphibious operation would involve between 10,000 and 17,000 Marines, of which between 4,000 and 5,000 would go ashore and fight, said retired Marine Col. David Fuquea, a professor at the U.S. Naval War College.



Transporting that many Marines could take at least 20 of the Navy's 31 total amphibious ships, which would take weeks to assemble from the United States, said Fuquea, who teaches amphibious landings in World War II and military operational planning.



There are five or six amphibious ships permanently stationed in the western Pacific, Fuquea said. Even combined with a forward deployed Marine Expeditionary Unit that’s half of the number of ships that needed. The rest would have to come from the United States.



The real challenge is ferrying Marines and equipment from ship to shore.



"It’s because we don’t have a lot of landing craft — highlighted by the fact that the USS America, the new [landing helicopter assault ship], does not have a well deck," Fuquea said.



American and Republic of Korea Marines sight in side-by-side in front of South Korean Assault Amphibious Vehicles during a training exercise at Suseong Range, South Korea. Photo Credit: Cpl. Amaia Unanue/Marine Corps

In addition, coastal defenses have advanced significantly since 1950.



Advanced weapon systems can destroy ships and landing craft hundreds of miles from enemy coasts, but the Marines would have to putter ashore in landing craft that move at the same speed as they did more than 60 years ago, he said.



"They’re slow; they don’t carry a whole lot and, consequently, the amphibious ships would be at a much greater level of threat from the very prolific numbers of surface-to-surface cruise missiles out there that are being used around the world," Fuquea said.



A 'real alliance'



If the conflict continued for months, the bulk of the fight would turn to the armies of the U.S. and South Korea.



Tom Spoehr, director for the Center for National Defense at the Heritage Foundation and retired Army lieutenant general, said as weeks and then months passed, the United States would have to build combat power over time.



The whole mission of the U.S. Army would become preparing brigade combat teams for deployment, Spoehr said.



He said that the BCT in Kuwait would likely stay to maintain stability in that region, but those in Europe could shift to Asia, and Army National Guard units would be called up to fill in where active Army soldiers had left stateside.



But long term, filling the ranks gets difficult, Spoehr said.



"The perception is that if we need more brigades, we’ll just grow them," he said. "What we found out in 2007-08 in Iraq when we tried to grow the Army is it took about two years to grow a brigade combat team."



The defining aspect of a second Korean war would be the primary contribution from the South Korean military, which would play a role that the U.S. has not seen in recent years.



"This is truly a combined fight," Maxwell said of U.S.-South Korean mission. "We’re not talking about Iraqi forces or Afghan forces partnering with the U.S. We are talking about a real alliance, where the bulk of the fighting will be done by our alliance partner."



Staff writers Stephen Losey, David Larter and Andrew deGrandpre contributed to this report.



