The Villainess Enjoys a Carefree Married Life in a Former Enemy Country in Her Seventh Loop - Chapter 102.2: What the Young Hand Desires

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.

Spot was summoned from his comfortable charging pad and familiar floors to a world of magic and intrigue. After the flight of his new patrons, he is left to care for a filthy castle. During his quest to keep this new home clean, he will face demons, foreign armies, and the dreaded stairs.All those who stand before him will be swept away. Those who follow his spotless trail will find enlightenment, purity, and a world on its knees.Follow this wholesome vacuum on his quest to power.

In the residence of the Duke of Zhenguo, the legitimate young miss, known for her icy demeanor, had transformed overnight.She, who usually regarded no one, woke up to confront anyone she saw with a few harsh words, using her frail body to intimidate so much that no one dared to touch her.Afterwards, this legitimate young miss began taking on retainers, nurturing powerful officials, engaging in commerce, and recruiting troops… Every act so shocking and audacious, it defied the norms and provoked fear in all who spoke of her!Yan Wanqing was seen as an enchantress and a disaster by the people, a thorn in the flesh and a nail in the eye that the ministers wanted desperately removed, an entity everyone shunned as if she were a venomous snake.Only the Crown Prince Mingyue, descending from the divine altar, in the dark, godless alleys, grasped her neck and repeatedly asked her, “Will you marry me or not?”

[Gunfight + case-solving reasoning + decisive killing]

“I’ve been black and white, and you said I was an undercover agent???”

When Dean woke up, he opened his eyes and saw the scene where the robbers were sharing the spoils.

Because of the confusion of the original owner’s memory, Dean mistakenly thought that he was a real robber, so he chose to eat black and white, and emptied the magazine with an American-style Juhe.

Just when he was about to take the money and leave.

A blond beauty came to the door: “Dean is an intern police officer. The bank in the town was robbed. I ordered you to investigate the suspect. You don’t want to fail your internship, do you?”

It turns out that I am an undercover agent!

Dean is numb…

- Description from novelbuddy