The U.S. military has been developing war plans for North Korea for years, but a real-world fight with the nuclear-armed regime would not go down the way it’s being strategized, the top Marine said on Thursday.

Saber rattling between the U.S. and North Korea — intensified by a slew of intercontinental ballistic missile tests by the hermit kingdom — have put the Korean peninsula on edge. Analysts worry a catastrophic war between the two nuclear-armed states could break out at any moment.

The U.S. military has been preparing by posturing forces, prepping logistics and conducting numerous military exercises with partner forces in the region. Military commanders have been familiarizing themselves with the geography and plans of a potential land campaign, Gen. Robert B. Neller, the Marine commandant, told audience members at a discussion held by the Center for Strategic and International Studies.

“There’s plans out there that have been developed over the years,” Neller said. “If it were to go down, I am not sure it’s going to go down the way we planned it. It never does.”

A potential war on the Korean peninsula would involve a conventional land campaign but would be compounded by the prospect of nuclear weapons, massed underground artillery and a North Korean military committed to the fight.

“However it turns out, it will be a very kinetic, physical, violent fight over some really tough ground, and everyone is going to have to be mentally prepared,” Neller said.

In late December, during a visit to Norway, Neller told Marines stationed there as part of a small rotational task force to be ready for a “big ass fight,” according to Military.com. The controversial remarks received some pushback by President Trump who later said there was no “big ass fight” coming in the near future.

“I said there was a big ass fight coming,” Neller said Thursday. “The moral of the story is when you fly all night and you go to Norway and there’s only four hours of daylight, just be careful what you say.”

Nevertheless, the Corps is still prepping for one.

After nearly 17 years of operating in low-intensity counterinsurgency conflicts, Marines are now going back to the basics of combined-arms training for a conflict with a more capable North Korea.

In a future fight, Marines will need to go back to worrying about an electromagnetic signature, camouflaging positions and night movements. They would be ever more conscious about the amount of radio chatter and radio frequency emissions emanating from tactical operation centers that could give away a position or make them vulnerable to jamming by a more sophisticated adversary.

“I hope it doesn’t happen, I don’t want it to happen,” Neller said, about the prospects of war with North Korea. “It would not be good for anybody.”

But the Corps has to prepare for these contingencies, even if the “big ass fight,” never comes. Being able to show the enemy what the U.S. will do to them if war comes is necessary for deterrence, and that means being ready at all times.

“I’d love to tell them [Marines] that nothing is going to happen and they can go to the beach,” Neller said.