The Reborn Otaku's Code of Practice for the Apocalypse - Chapter 172

After announcing it will be discontinuing all service, the internet game ‘Yggdrasil’ shut down… That was the plan, but for some reason, the player character did not log out some time after the server was closed. NPCs start to become sentient. A normal youth who loves gaming in the real world seemed to have been transported into an alternate world along with his guild, becoming the strongest mage with the appearance of a skeleton, Momonga. He leads his guild ‘Ainz Ooal Gown’ towards an unprecedented legendary fantasy adventure!

He is an extremely wealthy empire president who is obsessed with his wife and loves to pamper her.

One day, the bodyguard came to report: “Master, the young lady has gone after her fiancé!”

“Master, the young lady confessed her love live worldwide!”

“Switch the photo and name to mine!”

“Master, madam, go to the hospital to have the child aborted!”

The handsome and noble man was furious, “Get the young lady back to me so that I can serve her well! Stop, I will catch you myself!” [After Marriage]

Su Fu glared at her extremely possessive husband: “Get a divorce, we can’t survive this life!” Shangguan Ling smiled coldly: “It’s just that, whoever you don’t leave is your grandson! I will give you the property and the little buns, and I will give you the property.” Here you go! Wherever you go I will go too!” (Nuan Chong)

- Description from novelbuddy

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.

Kawaki, who was born in the dragon vein of a planet (Altana), first met Umibozu who was traveling in the universe, and his girlfriend, Kouka.Later, he came to Earth by accident and met the teacher who affected his life —Yoshida Shouyou.He also met a group of friends. The most conspicuous among the group of friends is a fool with silver hair and naturally curly hair, a short man with purple hair, and a little devil whose catchphrase is “Not Zura, it's Katsura!”Gintama Doujin, not transmigration.