The Main Heroines are Trying to Kill Me - Chapter 340: The Perfect Plan

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 general’s house, the eldest daughter is born again.

At home, she was invisible; after marriage, she was a decorative vase; in the end, a sea of flames buried her, and not even her corpse remained. This is the portrait of Han Yuxi’s previous lifetime.

Given a chance at rebirth, she strives to improve herself, wishing only to no longer serve as a foil or a pretty face. Then, she will seek out an exemplary husband and live a life of peace and prosperity. Alas, things turn out contrary to her wishes—she marries a man who bears a blood feud and hatred as deep as the sea.

She turns the world upside-down, but her road to happiness is strewn with setbacks and the sweetness that comes after bitterness.

- Description from Novelupdates

I got transmigrated into a game I’ve never seen before.

I thought it was a top-notch RPG and spent 30 years on it.

I retired as a war hero and planned to spend my remaining time leisurely.

But it turns out, it was an academy story?