Ace of the Dragon Division - Chapter 1158

Three Emperors have died in quick succession. The prince whom nobody had taken notice of unexpectedly succeeds to the throne. He is quickly plunged into layers upon layers of danger. The Empress Dowager dislikes him, wishing to install a younger, more obedient Emperor. His half-brother dislikes him, accusing him of stealing the throne that is rightfully his. The palace attendants and servants dislike him, believing that he is not a true Emperor. The Child Emperor must save himself.

A tale about the former leader of a special organization served under royalty, now leaving his past life behind and unintentionally getting involved with the martial world.

- Description from Novelupdates

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.

I was on my way home with my friend when suddenly, I spotted a catgirl cosplayer who made my heart skip a beat.But something felt off—I couldn’t recall seeing her in any anime, manga, or games I had ever come across. Confused, I asked my friend standing next to me.To my shock, his response sent chills down my spine:“Huh? What catgirl? What are you talking about?”Suddenly, a truck came barreling toward the girl. Without thinking, I rushed to save her. In the end, both of us were hit by the truck.Now, I find myself reincarnated in another world—in the body of the very catgirl I had seen.But... who is this girl?How is she related to the dungeons that keep popping up in this new world?