I'm Building Cannons in the Western Regions

>Chen Wang, an assistant researcher at the Ordnance Research Institute, was brought to 121 BC by a sandstorm during a desert experiment. When he woke up, he was lying in a leaky earth house in Dunhuang, covered with a moldy linen blanket. His only property was an old-fashioned watch that had stopped working... Huo Qubing stood on the city wall and looked at him, and then said to him: "Follow me." From then on, the cavalry of the Han army had telescopes and flags, the scouts had improved bows and gunpowder arrows, and there was an army "that could breathe fire" on the grasslands of Mobei. But Chen Wang has been waiting for one thing - when will the signal bar on his mobile phone light up again...