Siheyuan (traditional courtyard house): Starting with the Korean War, returning home to take charge

When the phone rang, He Yuzhu was staring blankly at the curvature advancement plan. The ashtray on the table was full, so he stubbed out his cigarette and answered it.

"Hey, the exoskeleton prototype is all assembled. Would you like to come and take a look?" Chief Engineer Zhao's voice was tinged with excitement, like the tone He Nianhua used when dismantling firecrackers during the Chinese New Year.

He Yuzhu glanced at the calendar on the table. Two weeks had passed since the curvature advancement meeting. He stood up and stuffed the proposal into the drawer.

"What time is it?"

"Ten o'clock. Research Institute playground."

He hung up the phone and walked to the window. The sky outside was overcast, threatening to rain. The big-character posters on the courtyard wall had long been torn down; the wall was covered in a layer of gray plaster, with a few pieces missing, revealing the blue bricks underneath.

The pebbles on the playground were scalding hot. He Yuzhu stood under the shade of a tree, looking at the silvery-white metal frame. The frame was taller than a person, with two legs, two arms, and a bare back. The motors were exposed at the joints, and the hydraulic rods were dark and grimy. The operator stood inside, encased in the frame, like a metal man.

Chief Engineer Zhao squatted to the side, clutching a tablet in his hand, his fingernails embedded with dust. Professor Liu from Harbin Institute of Technology stood behind him, his glasses as thick as the bottom of a beer bottle, the edges of his notebook tucked tightly into his hand.

"Chief He, are you ready?" Chief Engineer Zhao stood up and dusted off his knees.

He Yuzhu didn't speak, but nodded.

The operator took a step forward. The exoskeleton's joints hummed, the hydraulic rods extended and retracted, and the motors whirred. He walked to the large iron weight—five hundred kilograms, cast iron, dark and squatting on the ground like a heavy stone block. He bent down, grabbed the edge with both hands, and the hydraulic rods suddenly tightened with a hiss.

It wasn't the smooth, steady sound of hydraulic pressure. It was a sharp, metallic hiss.

Chief Engineer Zhao's expression changed. He looked down at the tablet, his fingers swiping rapidly across the screen. "The temperature is too high. The heat dissipation can't keep up."

He Yuzhu didn't move. He stared at the hydraulic hose, watching it bulge little by little, like a snake about to burst.

The operator gritted his teeth and lifted the weight. His arm trembled—it was hard to tell whether it was the exoskeleton or his own muscles shaking. The weight lifted off the ground, suspended in mid-air. Some of the people standing by the playground gasped, while others took a half-step back.

He Yuzhu's breathing stopped. Not out of fear, but something indescribable—like when Xinghe-1 first successfully completed its mission, his heart skipped a beat. He stared at the iron weight supported by the hydraulic rod, his fingers clenching at the seam of his trousers, then releasing.

The operator carried the weight ten steps. Each step was steady, but He Yuzhu could see that his knees were slightly bent, as if bearing a weight they shouldn't be carrying. The weight landed, the ground shook, and a small cloud of dust rose. The hydraulic hose retracted, the bulge disappeared, but a few drops of dark yellow oil seeped from the hose wall, starkly against the silvery-white metal.

Chief Engineer Zhao leaned over, wiped it with his sleeve, and more seeped out.

"The sealing ring can't withstand high temperatures." His voice lowered, as if he were talking to himself.

He Yuzhu didn't reply. He walked up to the operator and stared at the military green battery box. The plastic casing felt a little hot to the touch. He unscrewed the lid, revealing a row of lithium batteries wrapped with tape, their dense wires resembling a tangled mess.

"What about the battery life?" he asked, his voice lower than usual.

Chief Engineer Zhao flipped through his tablet. "Four hours. 150 kilograms of load, plus the operator's own weight, over 200 kilograms. The motor and hydraulic system can handle it—but the battery can't."

"Four hours?" He Yuzhu didn't look at him, tapping his finger on the edge of the battery box. "That's enough for one battle, but not enough for a day."

Chief Engineer Zhao opened his mouth as if to say something, but then swallowed it back.

Yang Xiaobing walked over from behind. He didn't speak, but first reached out and touched the joints of the exoskeleton. His fingers brushed against the gap between the metal and the hydraulic pipes, then withdrew, as if burned by something.

"Commander..." He paused, as if searching for words, "Four hours is enough for a surprise attack. But what if we get stuck in a stalemate? If the power goes out halfway through, this thing becomes a sitting duck. It can't run, can't lift its gun, and can't even take it off."

He paused, then lowered his voice even further.

"Soldiers are not machines."

He Yuzhu didn't turn around. He stared at the battery box for a long time.

The operator emerged from the exoskeleton and crouched on the ground, panting. His clothes were soaked through and clung to his body, revealing the outline of his shoulder blades. His face was flushed, and beads of sweat dripped down his chin.

"One more time?" Chief Engineer Zhao asked.

He Yuzhu shook his head. "Let him rest."

He turned around and walked to the row of poplar trees at the edge of the playground. Yang Xiaobing followed him and offered him a cigarette. He didn't take it.

"Commander, are we really going to give this to the soldiers?"

He Yuzhu didn't answer. He looked at the silver-white metal frame in the distance, standing alone in the center of the playground, like a robot without clothes.

"Start with ten sets. You train people on them. We'll fix the battery issue as we practice."

Yang Xiaobing put the cigarette away and nodded.

Ma Yuejin squeezed through the crowd, clutching a small, silver-white metal box. He handed it to He Yuzhu gently, as if handing over something fragile.

"Dean, this is a prototype of a fusion battery. It's about the size of a palm and can power a building for a day. But to install it on an exoskeleton..." He paused, "it will take at least two years."

He Yuzhu took the box and weighed it in his hand. It was heavy. Three times heavier than a lithium battery of the same size. He handed the box back to Ma Yuejin.

"Two years, wait."

Ma Yuejin took the box and put it back in his pocket.

Yang Xiaobing stood to the side, looking at the box, his Adam's apple bobbing.

"Commander, two years... the soldiers can wait, but the enemy can't."

He Yuzhu didn't turn around. He stared at the exoskeleton on the playground, at the battery indicator light that had been turned off, and stood there for a long time.

"Let's start practicing."

He turned and walked towards his office. His footsteps were heavy, crunching on the gravel path. The sun was setting, casting a long shadow. Yang Xiaobing stood there, watching the shadow recede into the gray sky until it disappeared into the distance.

That evening, He Yuzhu sat in his office and took the list out of his drawer. Turning to the page on "exoskeletons," after the words "debut," he added a line: "Jointly developed by China North Industries Group Corporation Limited and Harbin Institute of Technology; 500 kg load capacity; 40 km/h speed; 4-hour endurance. Ten sets will be deployed to special forces units. Miniaturization of the fusion battery will take two years."