Abyssal Sovereign: The Demon's Dominion - Chapter 99: The empress..

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.

In the myriad realms, legends rise and fall in the countless eras.

In a world of Mana Awakened powerhouses, Damian Bloodbane awakened into the Legendary, never-seen-before and utterly shameful E-Rank.E-rank.Before Damian Bloodbane, D-rank was the lowest Grade among all of the Mana Awakened in the entire world.After Damian Bloodbane, the world had its first and only E-rank Mana Awakened.It was worse than being Unawakened.The scorn, the ridicule, the mockery, the sarcasm and the utter humiliation he had to go through nearly drove him mad.Until one day…[Death Energy Detected… Absorbed][Necromancer King System Activated][Welcome, Damian Bloodbane, Sovereign of Death][You may select your class][Available Classes:][Death Necromancer][Death Knight][Death Assassin]Witness the rise of Damian Bloodbane from the Legendary E-Rank Trash to be the World-Strongest King of Necromancers! Or… will he?

Our straight (?) bottom woke up ten years into the future and found himself on the bed of his childhood friend… At the start, the bottom was shocked to his very bones, but he soon quickly accepted this premise and found the whole situation to be rather amusing. Precisely then, the bottom once again went back to his timeline — back to when he and the top were just platonic childhood friends.

Landmines include but are not limited to: Sweet & naive bottom, a president story, logic is dead, slow-progressing romance, the protagonist’s name has too many character strokes, the names are hard to pronounce, too many gay characters…

- Description from novelupdates