Toaru Majutsu no Index - Volume 1, Chapter 4: The Exorcist Chooses the End. (N)Ever_Say_Good_bye.

In a world where Magic reigned supreme, Ruling over the Mythic Elements were the Holy Magicians of the Sacred Elements.

A young prodigy, Gabriel was selected as the Holy Priest in the Church of the Magic of Light. He was the youngest mage to awaken the most coveted element of light; his future was supposed to be bright... But one day, he disappeared as if the darkness had swallowed him up.

As Gabriel walked on the thin line between life and death while fighting for his life, something came in his life... Something that was going to change his life and the world forever...

Step on this unforgettable journey of light and darkness that transcends boundaries of space and time like never before...

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.

Lugh woke up to find that he had transmigrated to a hundred million years later.