Don’t Concern Yourself With That Book - Chapter 211

An underprivileged prodigy, a cruel, ruthless world, and an epic story of battle and conquest. A young man with an exceptional inheritance leaves the small, rural city from which he hails on a journey to find the girl of his dreams. He defeats countless prodigies, sweeps through all forces that dare to stand in his way, and progresses step by step toward the pinnacle of all the worlds!
“I’m not targeting any gods in particular. All I’m trying to say is that all gods are trash in my eyes!”

- Description from Novelupdates

Collapsed without warning, and upon awakening, he found himself back in his childhood.He thought it was a blessing from above, but unexpectedly, tumultuous changes ensued, shrouded in mystery...

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 soldiers’ mercenary group where he used to work had been utterly destroyed, Loren, who survived the disaster, decided to walk the adventurer’s path as a way to make a living. However, for Loren who had no acquaintances and nothing but an empty pocket on him, receiving a single quest seemed like a faraway aim. So, as he was contemplating about what he should do next, another adventurer called out to him.