Owari no Chronicle - Volume 12, Chapter 14: A Place of Old Memories

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.

The price for saving the world is the right to rule it. After saving a faraway land, Lyn Rivers was cast back to Earth. Wanting the admiration, prestige, and glory of saving that realm, she forced her way back. But she was forgotten, and someone else claimed credit for her deeds. Now, with the power of a deity of destruction, she desires nothing more than to claim her place in history. To do that she will conquer dungeons, make alliances, destroy kingdoms, and build an empire. After all, why ruin the world when you can bend it to your will?

Gu Qingmo began to disguise herself as a man because of a word from her master.

Later, because of the words of my brother, I tried not to open my mouth if I could.

Later, I don’t know why the whole cultivation world is talking about the old master of Wanjianzong, the closed disciple of Xiaoyao Sanren, who is cold-hearted, taciturn, self-restrained and respectful, and who cultivates the ruthless way.

Mo Chuli thought so until she died in her hands.

However, since he was reborn and accepted as a disciple by Gu Qingmo, he discovered that——

Well said, cold hearted! taciturn! Self-denial!

It’s all an illusion!

Small snippet:

The day before Gu Qingmo was going to take Mo Chuli out for a training session, the headmaster made a special trip to Jianfeng and said to Mo Chuli, “Chuli, my uncle told you that if your master wants to go out in the future, you will definitely to follow.”

Mo Chuli: “Sect Master, why is this?”

Liu Qingbai: “Your master’s words are easy to offend people, so you have to keep an eye on it.”

Mo Chuli: “…”

[Woman pretending to be a man to decorate the real world’s first upright and paralyzed heroine × Seizing the house after her death was accepted by the heroine as an apprentice and the former Demon Lord hero]

ps: The female protagonist has a ceiling level of combat power, and the male protagonist is a growth type

- Description from novelbuddy

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