MTL - Everlasting Sword God - Chapter 51 Xiao Long Zun

Chen Yan travels between worlds, ending up becoming an honorable prince in a medieval fantasy world. Yet this world was not quite as simple as he thought. Witches with magical powers abound, and fearsome wars between churches and kingdoms rage throughout the land.

Roland, a prince regarded as hopeless by his own father and assigned to the worst fief, spends his time developing a poor and backward town into a strong and modern city, while fighting against his siblings for the throne and absolute control over the kingdom. Join Roland as he befriends and allies with witches and, through fighting and even farming, pushes back invaders coming from the realm of evil.

- Description from Novelupdates

When he first crossed over, Chen Liguo did not want to accept it.

Shen Yansheng always thought that she didn’t like Lu Jingce until one day she heard that a certain group boss intended to marry his daughter to Lu Jingce. She was so angry that she couldn’t eat anything that night and locked herself in the room after returning home. When Lu Jingce came back in the evening, he took the key from the study, opened the door and entered her bedroom. He sat beside the bed, leaned over and kissed her to wake her from her sleep. She looked at him angrily, but he smiled happily and asked, “Jealous?”

Shen Yansheng and Lu Jingce have been falling in love all the time, mainly because she hadn’t figured out how to explain their relationship to her parents, which caused her parents to always think she was single, so they took the initiative to trick her into going on a blind date. But someone happened to have a dinner in that restaurant that day, and saw her and her blind date sitting at a table for dinner from a distance. She felt a gaze looking at her from behind, and when she turned her head, she met someone’s handsome face that was half-smiling. That night, as soon as Shen Yansheng came home, she threw herself on someone, raised her hand and swore, “I can explain it!” Someone still had that half-smile and pinched her cheek, “The explanation is invalid.”

- 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.