Itai no wa Iya nanode Bōgyo-Ryoku ni Kyokufuri Shitai to Omoimasu - Chapter 50

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.

Luo Yi, a high school dropout in his original world, was isekai’d into the world of the Witcher 3. Starting out as a weak boy named Roy in the village of Kaer, Lower Posada, he was determined to grow stronger, no matter what it took. The first step toward becoming a legend was to kill. And his first kill was… a rooster. ‘You gain 1 EXP.’ Of course, Roy had his own cheat system like all the other isekai protagonists. His first step to becoming a legend started now…

System: Host, what is that thing in the sky?

Shi Sheng: An intergalactic spaceship.

System: …This is a cultivation world, where did an intergalactic spaceship come from?!

—

System: Host, what are you holding in your hand?

Shi Sheng: Xuanyuan Sword.

System: This is an advanced scientific world, where did an ancient divine sword come from?! Wait a moment… Host what are you doing?! Σ(°△°|||)︴

Shi Sheng: Breaking apart the main couple. ヾ(^▽^*)))

#MyHostIsTooPowerfulAndLikesToBreakShips#

Note : ‘shipping’ is the term people use when they want two people to be a couple.

- Description from novelupdates

【Survival + Wasteland Reclamation】

Welcome to Survival World!

Here, forget everything you once had and try to live!

In the beginning, there is no tool other than a tree house seed, but you need to find hope in this dangerous jungle.

[Unlocking the creator permission of Survival World…]

what’s the situation? !

[Creator permission unlock failed…]

What is the situation? ? ?

- Description from novelbuddy