Tensei Shitara Slime Datta Ken (WN) - Chapter 17 – The Outcome of the Promise

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.

Yang Tian, a Legendary Beast Tamer who tamed Legendary Monsters such as the Six-Wing Purple Gold Lion, the Undead Lich, and the Thousand Feet Ghost Vine has returned to three days before the Post-Apocalyptic Era begins.

Big news: Fu Xuechen, the great God of mathematics department, is making friends with the little cutie of the Chinese department.

Her roommate pressed her: “I heard that the great God is chasing you!!!”

Ran Xing with a blank face: “He didn’t chase me!”

Her roommate asked, “What is he looking for you?”

Ran Xing looked at the sleeping God: “Lying on the desk next to me and sleeping.”

Roommate: “…”

Fu Xuechen is a patient with severe insomnia. His dark circles are comparable to those of Gaara. He was prepared for sudden death long before he met Ran Xing.

But after one look, he fell asleep on his desk.

He simply asked for her timetable and slept next to her every day.

Later, Ran Xing rented a house outside. Her roommate asked her for something and rang the bell. But Fu Xuechen, who was only wearing pajamas, opened the door.

The roommate quickly apologized: “Sorry, I went to the wrong place.”

Fu Xuechen said lazily: “You didn’t go wrong. She’s inside!”

Roommate: “…”

She said that the great God did not chase her!!!

- Description from Novelupdates

You take up a student career.

Student career upgrade to lv.7

Acquired skills: primary school knowledge, junior high school knowledge, high school knowledge.

You take the college entrance examination,

You got a perfect score.

Your basic occupation has been upgraded to lv.9, and the job transfer system has been activated.

You change jobs to become a scientist, you gain R&D skills

You use research and development skills to get space fortress construction technology

You use R&D skills to gain starship technology.

You are invincible.

- Description from novelbuddy