While on the campaign trail in West Virginia last year, Donald Trump donned a hardhat and pantomimed digging coal with a shovel. The coal miners in the audience would soon be back to work, he promised: “Get ready, because you are going to be working your asses off.”

The only problem: Coal miners no longer swing a pickax or wield a shovel. While coal companies are hiring again, executives are starting to search for workers who can crunch gigabytes of data or use a joystick to maneuver mining vehicles hundreds of miles away.

“If you do PlayStation, you can run a 300-ton truck,” said Douglas Blackburn, a fourth-generation miner himself who runs the industry consultancy Blackacre LLC. For an industry once notorious for its risks, “the worst that can happen is you sprain a thumb.”

The trend toward fewer workers, of course, is nothing new. The heyday of coal employment came in 1923, when the U.S. industry — then reliant on laborers with hand tools, blast powder and oil lamps — had a record 863,000 miners, according to the Mine Safety and Health Administration.

Ever since, that number has fallen thanks to increasingly sophisticated machinery. The technological change took a leap forward in the 1980s with the expansion of large-scale mining in Wyoming’s Powder River Basin, where the coal can be scooped out of the ground from above. The miners no longer had to tunnel underground.

In the Powder River Basin’s giant open-pit mines, large haul trucks now crisscross the sites day and night, collecting up to 400 tons of coal at a time from towering seams. High-school graduates with little experience often drive the trucks, taking home salaries that can be $30 an hour. Trains that can stretch more than 100 cars long are loaded up mechanically with the coal and sent off to plants as far away as Georgia.

“Whether coal comes back or not is not necessarily directly related to jobs,” Heath Lovell, a spokesman for coal producer Alliance Resource Partners, said in an interview on NPR’s “On Point.” “We should be becoming more and more efficient, which would mean we could produce the same amount of coal with less employees.”

In Illinois, underground miners including Alliance Resource and Foresight Energy have a collection of longwall machines — computerized devices that cut coal from the earth in slices that can extend for miles — ready to ramp up production with minimal manpower if demand allows.

To be sure, Trump’s pledge has come true for some workers. Coal companies added 2,400 jobs since September, bringing the total to 51,000, according to the Bureau of Labor Statistics. Coal companies are advertising for licensed mechanics and electricians, warehouse clerks and security guards.

Coal’s future, however, is likely to involve a new set of skills. It won’t be long before a miner is working out of an office in, say, Denver, where she’ll stare at computer screens and maneuver equipment in Wyoming, according to Blackburn. The miner — earning, perhaps, $15 an hour — will monitor several massive trucks that largely steer themselves, he said.

Just as electric locomotives once replaced the pit ponies and mules in the mines, Caterpillar Inc. is already selling fleets of its “autonomous” haul trucks to Australian mining companies. One customer, iron-ore giant Fortescue Metals Group Ltd, has increased productivity by up to 30 percent thanks to the vehicles’ better-than-human consistency and precision, Denise Johnson, Caterpillar’s head of resource industries, said at a Deutsche Bank summit on June 8.

“You can keep those trucks running 24/7,” Johnson said. “You don’t have to take bathroom breaks.”

That sort of savings will be hard for U.S. coal companies to resist as they struggle to stay competitive against the onslaught of cheap natural gas, solar and wind power. Caterpillar’s autonomous-mining technology is already being adopted by U.S. customers and it’s expanding its offerings, a company spokesman said by email. The company declined to identify its customers.

And such technology won’t be limited to Wyoming. When talking to coal executives, Rick Honaker, chairman of the University of Kentucky’s mining program for the past decade, keeps hearing how they want young engineers who can automate a piece of equipment, managing gigabytes of data so the machinery can be used most efficiently.

“The way to compete is being more automated,” Honaker said in an interview. “And unfortunately, that means less jobs — more skilled labor but less overall employment.”

Against that backdrop, Trump is capitalizing on the sense of nostalgia for coal’s bygone days and anxiety about the future, said Patrick Hickey, a political science professor at West Virginia University. In Appalachia, people are well aware that miners stopped heaving coal with shovels generations ago, but Trump’s air-shoveling still resonated in a state whose flag bears the image of a 19th century miner holding a pickax.

“Coal mining jobs were hard jobs — people had serious health problems as a result of them — but an honest effort was rewarded well,” Hickey said. By trading politically on an antiquated image of a miner, Trump is appealing not just to displaced coal workers but to those in manufacturing and other sectors threatened by automation and foreign competition.

“As we see this disruption all over the economy in the public and private sector, I think it’s really powerful to hearken back to these touchstones of an economy that had more certainty,” he said.

One irony for the industry now is that in some areas the coal companies say they can’t find the high-skilled workers they need. In West Virginia, companies are resorting to offering signing bonuses and fully paid healthcare to poach experienced shift foremen, mechanics and electricians from rivals. Many of those workers left the coal industry during the last decade’s collapse and found more stable employment in other sectors. They aren’t anxious to switch back.

“The scars are still fresh,” said George Dethlefsen, CEO of Canonsburg, Pennsylvania-based Corsa Coal Corp., which opened a mine in Pennsylvania this month. “Those guys are not fully trusting that this market is back and here to stay.”

Finding young talent is especially hard. During the bust, companies were laying off people rather than training a new generation of miners. That created a dearth of high-skilled workers in their 20s and 30s.

“Youth might be the most looked-for qualification,” Matt Preston, a coal analyst at Wood Mackenzie Ltd., said in an email. Finding young workers “willing to get into a shrinking industry is an uphill climb.”

Bloomberg’s Jennifer A. Dlouhy contributed.