Maou-sama no Machizukuri! ~Saikyou no Danjon wa Kindai Toshi~ - Volume 9 Chapter 13

Before her rebirth, Wei Luo was an innocent little girl.

No family, no power, no inheritance — a thrice-lacking protagonist. Just how will the seed rise up from the mud?

- Description from Novelupdates

Sean: Hello, I look up to you like a torrent of river water, uh, can I shake your hand?

One day, he shook hands with Sean suspiciously.

Sean turned around and laughed wildly in his heart: Hehe, the top knight talent is in hand.

Knight fan group 835732045, if you are interested, you can add it.

- Description from novelbuddy

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.