Miraculous Doctor in Flower City - Chapter 206:

A magical ring and a mighty spirit inside the ring, coupled with a genius who lost his cultivation and got named worthless trash. That’s Xiao Yan, the poor genius. You think Xiao Yan got it bad? Well, you clearly have not met Jing Yan.

Jing Yan was once the shining star of the whole East City. However, his cultivation dropped because of the Universal Ring that was left to him by his dead grandfather. Without anything but the Universal Ring, he will once more rise towards the top and beyond!

He is Jing Yan, The Universal Sword God.

- Description from Novelupdates

Gu Jiuyi accidentally time-traveled to ancient times, which was already quite inconvenient, but then she also encountered a great disaster. With no other choice and to survive, Gu Jiuyi had to cling tightly to the benefactor’s leg. Following her young benefactor, she fled the famine without panic. How to deal with disease, hunger, wild beasts, and evil people all at once? Bring it on, let’s showcase our ten all-around abilities, plus the system space, everything can be crushed (Xie Zhan: You can’t even cook properly, yet you claim to have ten all-around abilities? Where’s your face?). We can even lead everyone to prosperity and enjoy royal provisions.When Gu Jiuyi was enjoying the happiness of being a single wealthy lady, her young benefactor cornered her against the wall: Come with me to the palace, I’ll make you my consort.What the heck? I don’t want to engage in palace intrigues!

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.

To correct the mistakes of his past, a young man is forced to narrow the space between science and witchcraft, as he ventures on a quest to save his world from complete destruction.