Itai no wa Iya nanode Bōgyo-Ryoku ni Kyokufuri Shitai to Omoimasu - Chapter 15

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.

Just as Ye Fan got dumped by a gold-digger, he received a call from the hospital. Little did he expect that, ten months ago on one fateful night, he and his crush Bai Susu did something unspeakable… From that moment on, he embarked on the path of a doting dad… Pampering his wife, spoiling his kids… Unlimited affection!“Hello, Mr. Ye Fan, your wife is about to give birth in the hospital, hurry over to sign the paperwork!” An urgent voice sounded from the phone.“What, what’s going on, kid, and wife?” Ye Fan was utterly bewildered at that moment.… Just got dumped, then his biggest crush came knocking on his door.From then on, he embarked on the journey of spoiling his wife, spoiling his kids, unlimitedly! They had a grand wedding, everyone in town joined in the love fest! As the saying went, good things should be shared together, not alonel! So, let’s all enjoy the love fest together!

Let’s fight! Go! Who am I afraid of with a chip that turns into a brain cell? ! Get promoted and get rich! The nest treasures are all mine!

- Description from novelbuddy

Roan transmigrated as an FBI investigator.Several years later, a journalist interviewed the world-renowned detective Roan Greenwood and asked,“What made you persist in solving cases for so many years?”Roan tilted his head and glanced at the sports car beside him, the villa behind him, and the beautiful woman inside the villa. He smiled slightly and said,“Well, the bonus after solving the case.”“What?”