Shini Yasui Kōshaku Reijō to Nana-ri no Kikōshi - Chapter 152 - The Cave Castle’s Wolves (part one)

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.

Yu Zhengdu joined a small start-up company that claim to offer “life management services”……as a programmer.

On his first day in office, he received a phone call from a stranger: “Hello, I received a text message from your company that informed me of my reincarnation tomorrow……”

Yu Zhengdu: “……??”

Shang Que, the beautiful little boss, said, “New employee, welcome to the Hell organisation in the human world. A thousand years ago, I was known to the human world as the Ghost King of Luofeng Mountain.”

Yu Zhengdu: “……??” From then on, he was incredibly distressed about the development of Hell.

- Description from Novelupdates

[Free New Book] The predecessor of the Immortal God reincarnate and reborn in the third year of high school. Based on the many exercises in the memory of previous life, he practiced again from scratch. There are many traces and treasures left by his previous life. To explore, he has to re-enter the peak of the earth!

- Description from Uukanshu

She was the most arrogant assassin in the world in the twenty-first century, yet in the end, she was unintentionally killed by her senior brother, resulting in her traveling to Bingzhou continent. The first step after she opened her eyes was to crawl out of the fecal drain and throw the woman who schemed her into the fecal drain. However, at this critical moment, she met a cold and arrogant beautiful man. Looking at his disdainful expression … She would always remember the words of this proud and aloof man. “Once my beloved wife has my child, I will seize Ming You Nation’s land for you and our son!”

- Description from Novelupdates