MTL - Rich Devil - Chapter 546 , I will send you

Kurono Maou is a high school student who is sensitive of his sharp eyes and bad expression. No girlfriend but gifted with friends in his own way, he had been living a peaceful life.

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.

Ever since she transmigrated, she was blessed with an inbuilt anti-poison detector.

Beep beep – What? Her father’s concubine was evil and her half-sister was vicious?
Beep beep – Ah! She was in an arranged marriage and her husband did not love her?

Who cared? She could kill those evil creatures instantly with her high intelligence.

Her unparalleled beauty attracted countless suitors and her popularity topped the charts. No one was immune, even the emperors and princes were all captivated by her…

- Description from Novelupdates

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.