Seirei Gensouki ~Konna Sekai de Deaeta Kimi ni~ - Chapter 129.2 : Battle of Outpost

A 34-year-old NEET otaku, chased out from his house by his family, found that his life is reaching a dead end. He then recalled that his life could actually have been much better if he had made better choices in the past.

Just when he was at the point of regret, he saw a truck moving at fast speed, and three high schoolers in its path. Mustering all the strength he had, he tried to save them and ended getting run over by the truck, quickly ending his life.

The next time he opened his eyes, he is reincarnated to a world of sword and magic as Rudeus Greyrat. Born to a new world, a new life, Rudeus decided that, “This time, I’ll really live my life to the fullest with no regret!” Thus starts the journey of a man yearning to restart his life.

It was started with a harmless request, “Jessica, clear out a room for Zoey, she'll be moving in with us for the time being.”Jessica's marriage soon ended when that 'guest' climbed up the ladder, from a guest room downstairs, to Jessica's bedroom, and then, her husband's bed.After losing in the fight for her husband's attention and love, Jessica realized it was time to wear back her garment of dignity and respect. She signed the divorce papers and left the country.Two years later, she returned as the heiress to a conglomerate, but her husband was at the airport, waiting to welcome her home.“When did I say I didn't love you, Jessica?” he asked.

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.