Espionage: You Were Told to Go Undercover, but You Summoned the Fourth Calamity

[Espionage + Transmigration + The Fourth Calamity + Decisive and Ruthless + Military + Hidden Ace + No Romance]

(The blurb keeps getting rejected, so please go straight to the story.)

Lu Yan transmigrated ten years ago to an era of war, where he became a scholar who knew nothing but how to wield a pen.

He was also a proud underground operative. After being persecuted by spies once again, he was about to be driven into a corner.

Luckily, he awakened a System and escaped with the help of The Fourth Calamity.

From then on, he deftly maneuvered between the spies and the Japanese invaders, summoning players now and then to ruin their plans.