I Can Accumulate Proficiency, Starting from Alchemy - Chapter 877 - 373: The Heavenly Gate Crumbles, The Gray Divine Turtle_3

Su Yan adored Xie Yu for many years and finally got what she wanted, but Xie Yu ran away on the wedding day, making her a laughing stock. At that time, Bai Xingfan appeared in front of her. He held a black umbrella in his skeletal hand to shield her from the heavy rain, and the other hand stretched out in front of her with a gentle and determined voice: “Don’t be afraid, still With me.” Su Yan was stunned with tears in her eyes for a long time, and finally, she reached out to Bai Xingfan.

- Description from Novelupdates

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.

Inexplicably reborn in the year 2003, having failed terribly in his previous life, the prevailing concern with Xu Tingsheng, that stands above all else, is none other than her. But alas, he is just months away from entering university, while she is but in her first year of junior high… Regarding this, all he can do is wait silently…for now.

A man was about to commit suicide and decided to search for a way to die on the internet, but then he found an odd site that asked a lot of questions and had a point based system that allows you to create skills for a character. He took interest in it, and when he was done setting his character, he was asked, “You will now be transported to a world with the settings you chose. Coming back is not possible. Do you still accept?” Without thinking much of it, he pressed YES and found himself in another world with the skills he chose to have.