MTL - I’m Just a Pharmacist - Chapter 51 mech game

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.

Seol Woon-hwi, the Blood Heaven’s Righteous Blade, rose to power, becoming second to none under the heavens, reigning just beneath the sky itself.Yet, at the height of absolute power, he finds himself returned to his past—back to his days as the scorned illegitimate child of the Everlasting Snow Palace.

Gu Qingcheng has a fiery temper and is a well-known little princess in Jiangcheng, and she has a good boyfriend who spoils her to the sky.

Only her boyfriend’s cousin, Huo Sicheng, opposed her everywhere, and the two were notoriously deadly rivals.

However, at the engagement banquet, when Gu Qingcheng regretted the marriage in public and announced that she was going to marry the disabled Huo Sicheng who was in a wheelchair, the jaws of all the guests dropped in shock.

Just when everyone thought that the couple would fight to the death in private, guessing that either one of them wanted to keep their husband widowed or the other wanted to keep their wife widowed, but the fact is…

“Husband, I’m stuck in traffic and come back a few minutes late. Open the door and let me in.” Gu Qingcheng knocked on the bedroom door with a pitiful expression.

“Sleeping in the living room.” Huo Shao’s indifferent voice came from the room.

“Honey, someone bullied me today.”

The person who bullied Gu Qingcheng disappeared the next day.

“Honey, they all say I’m so fierce.”

Huo Shao glanced at Gu Qingcheng, and opened his thin lips lightly: “They are talking nonsense, you are not fierce at all.”

From then on, Gu Qingcheng set fire to Huo Shao and handed firewood, Gu Qingcheng abused the scum and Huo Shao handed the knife, and the husband and wife worked together without getting tired.

Only Gu Qingcheng knew that before her rebirth, she was provoked and misunderstood by a scumbag to misunderstand Huo Sicheng. After her rebirth, she abused the scum and slapped him in the face, and loved Huo Sicheng with her life.

- Description from novelbuddy

An alien race invaded the Earth on June 6, 2128. At the midst of this war, many nations allied with the alien threat and the war nearly wiped out the rebelling humans of the planet. At the edge of mankind's survival, the United Nations Army launched its forces to eliminate the immediate stellar threats that loomed over Earth.

General Seeker Carlean, commander and leader of the mission, risked and gave his life to destroy the immediate stellar threat. The battle was won though Earth lay in ruins. Perhaps mankind will live to see a few years of peace before the alien threat returns to wipe out their existence.

At the immediate aftermath of the stellar battle, the fallen Seeker Carlean awakens and finds himself at aged 17, living the peaceful life he lived 16 years before he died.

So begins a new game in the battle for humanity's survival.