Supreme Casanova: Ultimate Harem System - Chapter 254 New System Mission!

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.

Known as the youngest academician-level senior engineer, Zhao Guoyang was reborn in the 1990s. In this era of economic globalization, with his extraordinary wisdom and extraordinary insights, he created one miracle after another and became a name that shocked the world!

Wisdom is condensed every bit, brilliance is created by sweat, and witness the rise of a great power!

- Description from novelbuddy

One day, Zhang Chenfei met a car accident. Fortunately, he didn’t suffer any serious physical injuries. However, due to the impact of the car crash, his brain’s perception of the real world had turned into that of the novel that he was reading prior to the accident. The thing that horrified his wife, Jiao Qi, was… the Smart Brain, Louis XIII downloaded a series of books which meant that his husband would turn into a different character each time!

How will our adorable little wife deal with this kind of husband who seemed to suddenly suffer from multiple personalities?

This novel’s plot focuses on Zhang Chenfei’s changing personality based from the characters in the books, and how his wife, Jiao Qi, deal with every character as he will have to act in sync with whoever his husband’s character is. This is per the advise of the private doctor since treatment of this special condition was still under research.

As they act out their roles, they will gradually discover and learn more about the other, which they’ve never known in their seven years of living together.

- Description from Novelupdates

Lin Fan acquired the Sign-in System that led him on the path of the life of a god-level nouveau riche.