My Dungeon Life: Rise of the Slave Harem - Chapter 1646.5

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.

Utsuro no Hako to Zero no Maria, or The Empty Box and The Zeroth Maria, tells the sinister story of Kazuki Hoshino, who is almost madly attached to his everyday life, and his antagonist Aya Otonashi, who suddenly transfers into his class—for the 13,118th time. She majestically announces to “break” him, without paying heed to anyone else around them.

Crossing over into the 1970s to become a little girl, not enough to eat or wear, no problem.On my left, a brother spoiling his sister, on my right, a childhood sweetheart who's a warm piece of eye candy.Behind me is a group of little followers, here come the beautiful and happy days.Male lead version: Hmm, seems like my little wife has arrived.

Xia Bohe, a D-class actress struggling to make it big, wakes up to find herself transmigrated as a supporting character in a novel she’s been reading.

In this novel, the main character married a successful, wealthy and sexy CEO only to end up divorced with a ruined career and ultimately losing her life.

With a second chance in life, Xia Bohe is not about to give up easily.

But wait, what is this Goddess System with its beauty and acting skills?

This can make things very interesting and fun as Xia Bohe navigates her way to success in her career and love life while getting rid of other pretentious cups of green tea in her path!