In the summer of 202X, around midday, a naval flotilla out in the Atlantic was suddenly rocked when a pillar of light shot up from beneath the waves. Shortly after, a cylindrical wall appeared from the pillar, nearly transparent and faintly shimmering in the sunlight. The closest vessel quickly found itself gently but insistently pushed away by the rapidly-expanding cylinder.

“Contact the nearest base. Tell them everything,” the ship’s captain ordered as he watched closely. To his surprise, when he looked closely he could see that the few birds in the area were also pushed away. The captain could only assume the same applied to the fish below. For just a moment he thought about the reefs and other such ocean fauna, but shook it off. He was military. There was no need to worry about anything below his vessels, save the odd submarine.

“What’ve we got?” the captain asked one of his officers.

“Nothing beyond what we can see with our own eyes, captain,” the young man hesitantly replied.

“What do you mean?”

“There’s nothing on scanners, sir. I’m detecting shifts on the ocean floor, and displacement of creatures in the water… but nothing inside of the event. All I can tell about it is that it’s expanding fairly rapidly. Permission to leave my post and try to touch it, sir?”

“Granted.”

The captain tried to suppress a smirk as he watched the officer dash away. He half-expected it to hurt until he remembered the birds. Looking down out the window, he could see the crewmember excitedly run up to the bow with a large pole.

“Complete lack of discipline, but I can’t blame the kid.”

On the deck, the crewman had reached the far end of the ship and carefully extended his pole. To his unwarranted surprise, the pole was swiftly pushed back by the rapidly expanding column. Within moments, Andrei Chekov had been thrown against the deck with a bloody nose.

The captain thoughtfully stroked his beard at the shenanigans. “What are you?” he muttered to himself. Just as he closed his eyes, he could swear he saw something inside the column of light, which had by now almost reached a kilometer in radius. It looked like a mountain with something sticking out the side, which didn’t make much sense to the captain, dimensionally speaking. He hadn’t paid much attention in math class, but he knew you couldn’t fit a mountain with a castle on the side of it into an area that size.

He looked almost as foolish as the crewmember bleeding on the deck when he spent the next two minutes trying to see the image again – by blinking like he was having a minor seizure.

“Captain? Is everything alright?” asked another crewmember.

“Did any of you see that?” the captain asked hesitantly.

“See what, captain?”

“It looked kinda like a mountain with a castle on the side. Noone?”

“I think I might’ve, captain.”

“Inform the others. Keep our distance from this thing. If that mountain is going to do what I think it’s going to do, we probably don’t want to be right on the threshold of this phenomenon.”

“Aye aye captain,” the crewmember acknowledged. “Base agrees. We are to hold relative position near the event and inform them of any changes beyond growth. Shall I tell them about the mirage?”

“Yes please.”

As the hours passed, the mirage flickered into view at an increasing frequency as the column of light slowly kept expanding.

Early the next morning, an island snapped into physical existence inside the then-enormous column. As the column faded away, the crewmembers of the surrounding ships could see three settlements – two smaller ones on the ground, and one more like a city surrounding a beautiful castle in a rough half-circle. The other half was blocked by the mountain that it was built against.

“Crewman Chekov,” Captain Hartnell called out.

“Aye captain?”

“Inform base: An island has appeared inside the column. We’ll build a small force from the various ship crews in the flotilla and make landfall in two hours.”

“Aye aye, captain.”

Like a well-oiled machine, personnel from each vessel shuffled around and made their way to a beach-like area. It was almost, but not quite entirely unlike a beach, and the strike force’s leaders, which included a curious Captain Hartnell, decided the island mustn’t have been an island before it appeared in the Atlantic.

What they saw when they went further inland surprised them all.

Ponies. Nothing but ponies. Most of them were clad in golden armor, some a darker blue. There were regular ponies, ponies with horns, ponies with wings, white ponies, gray ponies, ponies with spears and ponies with… the captain could barely believe it, as if he didn’t have enough trouble already – ponies with fresh apple pie. Just about the only thing they all had in common was that their armor looked ridiculously outdated, and they all had remarkably large eyes.

They seemed afraid, and the unicorns on the frontline projected what seemed like force fields to cover themselves and their un-horned comrades.

Unfortunately, Private Princip had a bit of a phobia regarding horses (he’d been bitten by one long ago) and, like his fellow strike force members, carried a rail gun. It was your typical electromagnetic coil that fired a small slug of metal at ludicrous speeds. They had become standard issue a few years back when the power supply problem was solved.

Even at near lightspeed, the metal slug merely knocked over the unicorn whose shield had been hit.

Much to the continued surprise of the staff officers watching Princip make a total ass out of humanity and shouting at him, a much larger, more horse-like creature majestically vaulted over the frontline. It was as almost large as a regular horse, with a pair of wings and horn, a near-white pink coat, a confusingly colored, even more confusingly animated mane, and impressive gold barding. She (it was quite clearly a mare) landed right between the toppled unicorn and Private Princip.

Five seconds later, the stupid git had fired again. Another slug connected cleanly with the alicorn’s forehead. A small smattering of royal horse blood clung to her ethereal mane as her head whipped back, but she remained standing. In fact, when she faced the human again, her forehead was as good as untouched, and she simply stared at the guy with a huge grin. Her horn flared up in a brilliant golden glow, and Princip found his rail gun gently but insistently pulled from his grip. The men formerly next to Princip found their good sense, broke rank, and pulled him away.

“Greetings, my… over-enthusiastic visitors,” the magnificent horse spoke in perfect English as she held the gun in mid-air next to her. “I believe you must be wondering what we are, how and why we are here? Allow me to introduce myself first, if I may. My name is Princess Celestia of Equestria, from the world of Equis. Who among you is in charge?”

The captains looked at each other, each as in-charge as the other. “Captain Sue, why don’t you go? Woman to woman?” Captain Hartnell offered.

“I could take that as sexist, Mr. Hartnell,” Captain Sue argued. “But I can see where you’re coming from.”

“I will speak for my colleagues, Princess,” Captain Sue called out as she walked to the frontline. “My name is Captain Mary Sue of the United States of America, from the world of Earth.”

“God, why’d she have to snowclone the horse?” Captain Hartnell facepalmed.

“Tis a pleasure to meet you, Captain Mary Sue. If we can trust your forces to lay down these interesting magnetics, you can trust mine to do the same, and we might discuss the answers to the questions I spoke of earlier.”

“That might be best, your highness. If my colleagues can join us, that is.”

“I see no reason why not.”

Author's Note

And here we go. Thanks to #fimfiction for all sorts of suggestions, corrections and whatnot -- mostly Dram.

You might wonder, why do I write about Celestia getting railgunned in the head when I have an outspoken opinion on dark/gore fics? And why isn't this one marked as such despite said scene? Well, that's because aside from a little blood, Celestia is perfectly fine in the end and noone dies, or is permanently damaged.

Names: Captain Hartnell, named for the First Doctor. Crewman Andrei Chekov, after Pavel Andreievich Chekov. Private Princip, suggested after the guy who shot Franz Ferdinand. Captain Mary Sue, obvious.

None of these are likely to be relevant when the intro's good and over. B)