Kumo Desu ga, Nani ka? - Chapter 10 Level Up!

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.

After the death of Fu Sinian, Yu Duo’s heart shattered into pieces. As his widow, she was the recipient of Fu Sinian’s massive amount of inheritance. She spent her days drowning herself with alcohol and was depressed all the time. She mourned her late husband with the companionship of her designer purses, designer jewelries, and money that could last her several lifetimes.

But only Fu Sinian knew the truth — that after his death, this woman hosted parties, lived in their mansion, drove expensive sport cars, traveled the world, and flirted with men. She was having the time of her life.

Fu Sinian wasn’t so angry that his soul dissipated; quite the contrary, he was so angry that he had come back to life!

Fu Sinian, who had come back to live, looked at the mourning Yu Duo and smiled devilishly.

“We are on! Watch me make you fall in love with me for real this time!”

- Description from Novelupdates

I was just your average burnout. Now I’m a kobold in a dungeon where everything wants to eat me—and frankly, I get it. I look delicious.Reincarnated as the weakest possible monster in the worst possible place, I start with nothing but panic, backward knees, and a skill called Civilization Mimicry—which is sealed. Because of course it is.But survival isn't the story.This is the story of what comes after.Of finding meaning in the scraps. Of building law from ashes. Of kindling memory in a place designed to erase.Because even if the world sees kobolds as nothing, I’ve seen what we used to be.And I’m going to bring it back.Firelight by firelight. Burial by burial. One fragile tradition at a time.Because if the world wants kobolds to be nothing?Then I’ll teach it what nothing becomes when it learns to dream.

Once the ultimate Soldier King and a supreme assassin, empowered by a magical Magic Bracelet, had mastered Cultivation, Medical Skill, X-ray vision, and foreseeing the future… became an omnipotent master of pretense. Come, come, come, watch the omnipotent master of pretense teach you a few tricks of pretense.A demonic man who walked out of a major foreign prison, yet married a cold Queen-like CEO wife, leading a life where “you glare at me with displeasure, and I look at you with disdain.”