Traveling back in time to Liu Feng, starting with rescuing soldier Guan Yu.

In the central command tent, only Liu Feng remained.

Liu Feng casually took a charcoal stick from the brazier, sat down on the ground, spread out the bamboo slips, and began to draw on them with the charcoal stick. His hand trembled slightly with the first stroke, but the second stroke was steady. His hand moved as if he were doing something he had done countless times before, the lines smooth and decisive.

Catapult.

Liu Feng had countless images of catapults in his mind. These included the reconstructions he had seen on video websites in his previous life, the models he had seen in museums, and the weight ratios that history buffs had debated hundreds of times on forums.

He didn't know which type of wood was best suited for making swing arms, nor did he know how to calculate the torque of the leather cable, but he knew the principle.

Lever. Fulcrum. Counterweight. Swing arm.

These four components combined would form a catapult capable of striking targets 300 paces away. Cao Cao's trebuchets used torque, resulting in a complex structure and difficult maintenance. What he wanted to build, however, was a counterweight catapult, with a swing arm, a counterweight on one end, and ammunition on the other. By releasing the latch, the stones could be launched.

Simpler, more reliable, and with a longer range.

Before long, Liu Feng had finished the last stroke on the bamboo slip, but he did not stop. The charcoal stick hovered in mid-air for a long time before falling again, and he began to draw a completely new shape on another bamboo slip.

Two arcs, two circles, and a horizontal bar.

Horseshoes. Something so simple, a bent piece of iron nailed to a horse's hoof. Yet this very piece of iron allows horses to run on gravel roads without injuring their hooves, and enables riders to make sharp turns on hard ground without slipping.

With horseshoes, a horse's lifespan would double, its marching speed would increase by 30%, and the rate of warhorse attrition would be greatly reduced. At this time, however, no one in this era knew what horseshoes were.

The Shu Han cavalry rode barehoofed horses, which had to rest every few dozen miles to prevent their hooves from cracking. Cao Cao's army fared no better; their warhorses suffered heavy losses, with more horses dying than men in a single battle.

If the Shu Han army could be equipped with horseshoes, even a thousand warhorses would be equivalent to two thousand.

Liu Feng continued drawing.

Stirrups. Not the single-sided stirrups used for mounting a horse, but double-sided stirrups. Made of iron, they hang on either side of the saddle, giving the rider's feet a foothold and making them more stable. Stability allows for wearing heavy armor more easily, wielding long weapons more skillfully, and drawing and releasing arrows more accurately and quickly!

Cavalry without stirrups can only be considered mounted infantry, while cavalry equipped with stirrups are the real iron cavalry, the tanks of the cold weapon era.

During this time, Liu Feng had come to know that soldiers in the Three Kingdoms period relied entirely on their legs to grip the horse's belly and one hand to hold onto the horse's mane to avoid falling off when riding horses. That's why Liu Bei lamented that his thigh muscles had "grown back" and that he had wasted his time when he was in Xinye; it was because he hadn't ridden horses for a long time and his muscles had atrophied.

With stirrups, cavalrymen could easily sit on their horses, freeing up their hands to do more things: slash, stab, shoot, throw, and even turn around on horseback to shoot arrows backward.

This is yet another example of a devastating attack.

After Liu Feng finished the last stroke, he threw the charcoal stick on the ground. The bamboo slip was covered with dense lines and markings. To an untrained eye, it would just look like a jumble of scribbles, but Liu Feng knew that this was arguably the greatest technological revolution on the battlefield of cold weapons before the age of gunpowder.

Liu Feng put away the three bamboo slips, sat back down at the table, and let out a long breath.

At Chenshi (7-9 AM), the tent flap was lifted, and Kou Zun stepped into the tent. He saw the bamboo slips spread out in front of Liu Feng and took a closer look.

"Brother, what is this?"

Liu Feng looked at him, a slight smile playing on his lips. It was an expression Kou Zun had never seen on his face before. It wasn't a smile, but a certainty, a confident certainty.

"Zirong, you've come at the perfect time. Gather all the blacksmiths in the camp and have them forge these two items according to the patterns on the bamboo slips."

Liu Feng rolled up the bamboo slips and handed them to Kou Zun. Suddenly, he lowered his voice and said, "This matter must be kept secret. All the craftsmen in the army must be gathered in one place to work on the project. Reliable soldiers should be assigned to supervise them. Once the project is completed, all the craftsmen should be taken back to Shangyong and their families should be kept under guard. I will decide their fate when I return."

Seeing Liu Feng's solemn expression, Kou Zun dared not ask any further questions. He immediately took the bamboo slip from Liu Feng's hand and said in a deep voice, "Yes, General."

……

Three wooden sticks, a bundle of hemp rope, and a stone.

Lai Dayan watched Liu Feng squatting on the ground fiddling with these things, his eyelids twitching. He had lived for forty years, seen craftsmen make crossbows and blacksmiths forge knives, but he had never heard of a trebuchet being conjured from a few wooden sticks.

Liu Feng first laid the longest wooden stick horizontally on the ground and tied the shortest one vertically in the middle as a support.

"Big Eyes, move that rock over here."

Lai Daye and his soldiers quickly moved the stone, which weighed about twenty pounds, over there. Liu Feng tied the stone to the shorter end of a long pole and then wove a bag out of hemp rope at the longer end of the pole.

"Watch closely."

Liu Feng stuck the wooden stick into the ground as a locking mechanism, pressing down on the short end of the long stick and pulling the long end down. The long stick was pressed into an angle, and the short end tilted up, suspending the twenty-odd-pound stone in mid-air.

"General...is this all?" Lai Daye and his soldiers stared wide-eyed.

Liu Feng kicked the latch open.

The long stick sprang up suddenly, the short end carrying the large rock to the ground, while the stones in the long rope bag were flung out. It flew through the air for a moment, then crashed to the ground thirty paces away, kicking up a cloud of dirt.

Lai Dayan's mouth was agape, and he couldn't close it for a long time.

"This...this is how you throw stones?"

"That's the principle behind the trebuchet," Liu Feng said, patting the dirt off his hands. "Lever. The closer the fulcrum is to the heavier end, the farther the lighter end can be thrown. The shorter and heavier you make the shorter end, the farther you can throw the stone with the longer end."

Lai Daye squatted in front of the wooden stick, looking at it again and again. Suddenly, he raised his head, his eyes full of surprise: "General, what if we replaced the wooden stick with a giant log, the stone with a boulder weighing several hundred pounds, and the rope with a cowhide rope..."

"Then it's not thirty steps," Liu Feng said calmly, "it's three hundred steps."

Lai Daye's breathing suddenly became heavy. He stood up abruptly, turned and walked out, but after two steps he turned back, knelt down and said, "General, you are truly a divine being! I am convinced! I will go find craftsmen right away and have it made tonight!"

"No rush."

Liu Feng handed him the bamboo scroll covered with lines, saying, "Make it according to this. The frame must be stable, the swing arm must be straight, and the weight must be heavy enough. The sling should be made of cowhide, and the tenon should be made of cast iron. Also, the base should have wooden wheels, otherwise it won't be able to move."

Lai Daye took the bamboo scroll, his hands trembling. He couldn't understand the lines, but he knew how much this scroll was worth—more than he could exchange for a city.

Liu Feng stood at the edge of the drill ground, watching Lai Daye and several craftsmen from the camp squatting on the ground studying the bamboo slips. The craftsmen were initially muttering to themselves, but after a few glances, their muttering stopped, replaced by an irrepressible excitement.

"Look at the angle of this diagonal brace—it's brilliant!"

"The drawstring is made with a three-strand braid, making it strong and unlikely to break."

"It's better to make the counterweight box round than square; a round one is easier to tumble over."

Liu Feng listened to the discussions, a slight smile playing on his lips. He didn't say much, only occasionally interjecting to point out key points. He knew he didn't need to do everything himself; he only needed to explain the principles clearly and illustrate the diagrams. The craftsmen would do the rest better than him. After all, they were the ones who made their living from this.

Around noon, the framework of the first catapult was erected. It was a behemoth, with a base ten feet square and a swing arm more than two people tall. The counterweight box was filled with stones, weighing over three hundred pounds. It took eight soldiers working together to push it to the center of the training ground. The wooden wheels rolled over the ground with a dull thud.

Lai Daye ran over, his face covered in sawdust and sweat: "General, it's finished! Want to give it a shot?"

Liu Feng looked at the expectant eyes of the soldiers in the camp and nodded.

A stone the size of a millstone was lifted into the rope, and four soldiers pulled on the ropes of the swing arm, shouting as they pulled it down. The swing arm pressed down inch by inch, and the counterweight box rose inch by inch until the locking mechanism locked in place.

Everyone on the drill ground held their breath.

Lai Daye stood beside the mortise and tenon, glancing back at Liu Feng. Liu Feng raised his chin. Lai Daye then brought his hammer down.

The latch popped open.

The counterweight box plummeted, the swing arm sprang up at a speed imperceptible to the naked eye, the rope drew an arc in the air, and the millstone-sized rock whistled away.

All eyes were on the stone.

It flew over the drill ground, over the camp, over the distant barricades, and crashed heavily to the ground. When the muffled thud echoed back, everyone counted: from the edge of the drill ground to the point of impact, it was at least three hundred paces.

The drill ground was quiet for a moment, then erupted into chaos.

"Three hundred steps! At least three hundred steps!"

"My God, this is farther than Cao Cao's trebuchets!"

"How high is the city wall of Rang County? If this stone were thrown, the wall would collapse!"

The soldiers shouted, yelled, and jumped around. Some knelt down to touch the stone that had been smashed into the ground, while others hugged their brothers and laughed heartily.

Liu Feng stood outside the crowd, watching everything. He remained calm. He knew the catapults were merely an appetizer. The real treasures lay in Kou Zun's hands: horseshoes and stirrups. These two items were what could truly change the fate of the Shu Han army.

Lai Daye squeezed through the crowd, ran to Liu Feng, bowed, and said, "General, is one enough? Should we make another one tonight?"

"Build them," Liu Feng said. "Build ten. Tomorrow at dawn, I want to see ten flying stone carts lined up outside Rang County."