Betrayed By My Fiancé, I Changed My Role From A Viscount's Daughter To A Lady-in-waiting To The Queen - Chapter 93: , Episode 18

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.

Lyle Walt is a young noble boy and heir looking forward to the day he can inherit his family’s territory. Except around when he was 10 year old, his parents started neglecting him more and more in favour of his little sister, Celes.
On his fifteenth birthday, he is challenged to a duel by his sister to see who will inherit the household and horribly loses, being cast out of his family. Afterwards, he gets treated by the family groundskeepers and receives the family heirloom Gem from him that Lyle’s grandfather had entrusted to him. From there, he begins an aimless journey with his childhood friend and former fiancée, Novem, and the Gem-turned-Jewel that houses the memories, personalities, and Skills of seven of his ancestors.

Ren Zhu: Quiet! Quiet! Look at the blackboard! I’m going to start teaching!

Bear child 1 [1]: Hahaha! Who is this weak chicken!

Bear child 2: May as well dance than listen to class. Why start the class!

Fake good child: Sit upright.

Ren Zhu: ……

Bear child 1: You received the class teacher’s quiet gaze x 1. Physical strength -500. Entered the weak state!

Bear child 2: You received the class teacher’s deep gaze x 1. Intelligence -50. Entered the mentally retar*ed state!

Fake good child: You received the class teacher’s gratified gaze x 1. Intelligence and physical strength +50. Entered the excited state.

Ren Zhu: My goal is to teach and educate people, and bring love to every bear child. Thank you.

- Description from Novelupdates

The first time he saw this woman, she was holding on the arm of an old man who looks like he’s about to enter the grave at any moment and smiling like a blooming flower;the second time he came across her, she was wearing a nurse’s uniform and flirting with a man; the third time that they met again, she appeared before him, as his blind date! Guan Ling Chao, the current prince (young master), an outstanding army officer, due to his family’s (elders’) threats to forced marriage, had no choice but to go on blind dates. Yet after meeting hundreds of different women, she was the only woman in the action group

- Description from Novelupdates