I picked up a book a year ago and read the summary at the back(part of a series maybe?) at a airport bookshop but had to stop because of my flight was about to depart. I can't remember the author or the title but I liked the plot and premise. Basically, the summary at the back of the book describes a soldier or marine or was it a unit? that was transported to a different reality that has magic/fantasy element in it. I know it's kinda vague but I hope you can help me out. I just found the plot so cool so anything close will be good enough for me.
Sounds like it could be Control Point by Myke Cole. From GoodReads:
Across the country and in every nation, people are waking up with magical talents. Untrained and panicked, they summon storms, raise the dead, and set everything they touch ablaze.
Army officer Oscar Britton sees the worst of it. A lieutenant attached to the military's Supernatural Operations Corps, his mission is to bring order to a world gone mad. Then he abruptly manifests a rare and prohibited magical power, transforming him overnight from government agent to public enemy number one.
The SOC knows how to handle this kind of situation: hunt him down--and take him out. Driven into an underground shadow world, Britton is about to learn that magic has changed all the rules he's ever known, and that his life isn't the only thing he's fighting for.
Glory Road by Heinlein?
The protagonist, a veteran called Evelyn Cyril "E.C." Gordon, nicknamed "Easy", responds to an newspaper ad promising "very high pay, glorious adventure, great danger" to people who are no coward.
He travels with Star, a beautiful woman he met previously, and Rufo, her assistant, to another world, on a quest to retrieve the Egg of the Phoenix. Adventures and a lot of swashbuckling follows.
After the quest is done, Oscar (as he is called now) gets bored and meets up with Rufo to take another journey down the "glory road".
Sir, the story your are writing about is titled "Rome Sweet, Rome" Popular Mechanics, October, 2011. The story which "originated" on Reddit was supposed to transformed to the silver screen, but it's having legal problems. Plus it seems the story is a hack of the 1979 Japanese film "G.I. Samurai".