Gekitotsu no Hexennacht - Volume 2, Chapter 2: Fun at Night

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.

# MYSTICALBEING # DNDThe Northern Ice Fields had no boundaries.The Winter Wolves hid within the snow, the Frost Tigers growled incessantly, and the roars of Giants echoed throughout the land. Many species struggled to survive in the icefield. At the same time, a baby White Dragon possessing the power of time broke out of its egg and opened its platinum-colored eyes.Years later, the legendary Time Dragon appeared, moving freely between the endless past, present, and future.

Ever since Yang Fan returned to the village, the young women had been practically breaking down his door...

Qin Chen crossed into Taiyi Holy Land as a sweeper, and at the age of sixteen awakened the system. As long as he signed in at different places, he could get different rewards.

Sign in at the Land of Emperor Ruins and get the world’s No. 1 Chaos Holy Body and the Chaos Emperor Sutra!

Sign in to seal the magic land and get the quasi-emperor soldiers!

Sign in at the Refining Hall and get the God-level Refining Technique!

Sign in at the medicine garden and get the medicine of immortality!

Sign in at the Imperial Palace and get the Emperor-level forbidden magical power ‘Resurrection from the Dead’!

…

Qin Chen thought that he would just sign in silently until the world was invincible.

One day, the relics of the Great Emperor will appear in the Holy Land, all the holy places, families, and ancient dynasties have come, and there will be an unparalleled demon king in the relics, killing countless powerhouses, ruling the world, and wanting to destroy the Holy Land.

In desperation, Qin Chen could only walk out, slapped the Demon King to death, and sighed: “I just want to be a sweeper and sign in silently. Why do you force me to take action?”

- Description from novelbuddy