Kyoukai Senjou no Horizon - Volume 7A, Chapter 19: Boy Attacked in a Hidden Place

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.

Under the starry sky, all races compete for the front.

The human youth Ye Huan has mutated eyes.

Don’t forget, it’s just basic exercises.

Martial arts, just watch it once.

If you read the exercises once, you are cultivating.

The medicinal pill came out after watching the refining process, and it could be optimized.

Yuanguo, Yuancao, the year has increased at a glance.

Ten thousand clan exercises and secret skills, just looking at them, they become human clan exercises and secret skills.

…

Under the starry sky, Ye Huan convinces all the tribes.

- Description from novelbuddy

I am a female secretary of an overbearing president in a typical dog blood drama text.

The kind of person who doesn’t have a name at the end of the day, and could only be called “secretary”, one who wears a tight fitting black dress and a pair of 10cm high heels every day, running around in front of the president, humbly praying for the president’s attention, and hating the heroine.

In fact, I really don’t. If I like the president, I’ll be struck by lightning.

I’m getting more and more sick of the president lately. Except for the outstanding appearance that the author forced on him, this person is really useless from head to toe, low in EQ, and low in IQ.

A legendary business genius who is all-powerful, but he doesn’t even understand anything, chickens know more than him.

I had to reject all of his unreasonable demands every day, and on the way, teach him relevant knowledge of economic law and finance, and gradually…he became a master.

I’m so tired, I really want to quit my job.

- Description from Novelupdates

Kael was once a being so powerful even the gods feared him—until he was thrown into The Null, a realm of endless torment and eventually cast into inexistence. But he returns, reincarnated as a powerless beggar in a broken world ruled by monsters and corruption.With memory of godly blood on his hands, he is determined to reclaim his strength, survive the Nexus's deadly trials, and tear down the heavens themselves.But it's a matter of time before the gods and celestials know he’s returned. And this time, they will not make the same mistake twice.> ◇ Ravager (Rank E) Eliminated. 20 VRP Gained.> ◇ 0.00109% Memory Unlocked. Forgotten Technique: Blight Shield Relearned.> ◇ Ather'valis, The God-Killing Blade, has been acquired.