Across the military, officers and troops are quietly preparing for a war they hope will not come.
At Fort Bragg in North Carolina last month, a mix of 48 Apache gunships and Chinook cargo helicopters took off in an exercise that practiced moving troops and equipment under live artillery fire to assault targets. Two days later, in the skies above Nevada, 119 soldiers from the Army’s 82nd Airborne Division parachuted out of C-17 military cargo planes under cover of darkness in an exercise that simulated a foreign invasion.
In perhaps the most incendiary exchange, in a September speech at the United Nations, Mr. Trump vowed to “totally destroy North Korea” if it threatened the United States, and derided the rogue nation’s leader, Kim Jong-un, as “Rocket Man.” In response, Mr. Kim said he would deploy the “highest level of hard-line countermeasure in history” against the United States, and described Mr. Trump as a “mentally deranged U.S. dotard.”
A false alarm in Hawaii on Saturday that set off about 40 minutes of panic after a state emergency response employee mistakenly sent out a text alert warning of an incoming ballistic missile attack underscored Americans’ anxiety about North Korea.
A Conventional Mission
After 16 years of fighting insurgents in Iraq, Afghanistan and Syria, American commanding generals worry that the military is better prepared for going after stateless groups of militants than it is for its own conventional mission of facing down heavily fortified land powers that have their own formidable militaries and air defenses.
The exercise at Fort Bragg was part of one of the largest air assault exercises in recent years. The practice run at Nellis Air Force Base in Nevada used double the number of cargo planes for paratroopers as was used in past exercises.
The Army Reserve exercise planned for next month will breathe new life into mobilization centers that have been largely dormant as the wars in Iraq and Afghanistan have wound down. And while the military has deployed Special Operations reaction forces to previous large global events, like the 2014 World Cup in Brazil, those units usually numbered around 100 — far fewer than some officials said could be sent for the Olympics in South Korea. Others discounted that possibility.
The Army chief of staff, Gen. Mark A. Milley, in several recent meetings at the Pentagon, has brought up two historic American military disasters as a warning of where a lack of preparedness can lead.
His concerns have drifted down to the Army’s rank and file. And troops at bases and posts around the world routinely wonder aloud if they will soon be deployed to the Korean Peninsula.
But unlike the run-up to the Iraq war, when the Pentagon had already begun huge troop movements in 2002 to prepare for the invasion that began in 2003, military officials insist that this is not a case of a war train that has left the station.
It is unlikely that the Pentagon would launch military action on the Korean Peninsula without first warning Americans and others there, military officials said — unless the Trump administration believes that the United States could conduct a one-time airstrike on North Korea that would not bring any retaliation from Pyongyang to nearby Seoul.
Some officials in the White House have argued that such a targeted, limited strike could be launched with minimal, if any, blowback against South Korea — a premise that Mr. Mattis views with skepticism, according to people familiar with his thinking.
“Even if no decision on North Korea has been made and no order has been given,” Ms. Flournoy said, “the need to be ready for the contingency that is top of mind for the president and his national security team would motivate commanders to use planned exercise opportunities to enhance their preparation, just in case.”
Operation Panther Blade
In the case of the 82nd Airborne exercise in Nevada last month, for instance, Army soldiers practiced moving paratroopers on helicopters and flew artillery, fuel and ammunition deep behind what was designated as enemy lines. The maneuvers were aimed at forcing an enemy to fight on different fronts early in combat.
Another exercise, called Bronze Ram, is being coordinated by the shadowy Joint Special Operations Command, officials said, and mimics other training scenarios that mirror current events.
This year’s exercise, one of many that concentrate on threats from across the world, will focus extensively on underground operations and involve working in chemically contaminated environments that might be present in North Korea. It will also home in on the Special Operations Command’s mission of countering weapons of mass destruction.
Beyond Bronze Ram, highly classified Special Operations exercises in the United States, including those with scenarios to seize unsecured nuclear weapons or conduct clandestine paratrooper drops, have for several months reflected a possible North Korea contingency, military officials said, without providing details, because of operational sensitivity.
During a briefing with reporters on Capitol Hill, Lt. Gen. Mark C. Nowland was asked whether the Air Force was prepared to take out North Korean air defenses.
“If you’re asking us, are we ready to fight tonight, the answer is, yes, we will,” General Nowland, the Air Force’s top operations officer, responded. “The United States Air Force, if required, when called to do our job, will gain and maintain air supremacy.”
The words were barely out of his mouth when Lt. Gen. VeraLinn Jamieson, the Air Force’s top intelligence officer, interrupted.
“I’ll also add that right now, the Defense Department is in support of Secretary of State Tillerson, who’s got a campaign to be the lead with North Korea in a diplomatic endeavor,” General Jamieson said.
General Nowland quickly acknowledged in a follow-up question that the military was in support of Mr. Tillerson’s diplomatic push.