July 7th, 2037.

One hundred years since the beginning of the Second World War.

Seemingly out of nowhere, the oceans that we once plied since time immemorial was denied to us by alien-looking beings, attacking shipping lanes, besieging entire island nations, blockading ports and naval bases.

Humanity's first military encounter with them resulted in a horrific loss, causing the assembled navies of the world to research new weaponry to counter their seemingly impenetrable hulls. Or more accurately, hides.

What we encountered are known post-facto as Abyssals. Beings who are as alien as they come, sporting jet-black armor and weapons, miniature drones whose firepower is able to blaze through entire fighter squadrons in no time at all, armaments which are able to pierce through even the thickest of hulls.

Many civilians died the moment they decided to make waves for the first time.

At first, there were no reliable footage of the Abyssals, as we soon came to call them. What the world saw were black blobs on the surface of the ocean, decimating frigate after destroyer after cruiser. For 3 long months humanity as a whole struggled against the Abyssal threat.

Then the greatest breakthrough of the war came on a certain sunny day on the shores of Okinawa. A combined USN-JMSDF task force aimed at breaking the blockade of the Ryukyu Islands and Taiwan chanced upon a corpse, later identified as a Wo-Class Standard Carrier by the Abyssal's own reckoning, floating close to shore.

When the world's scientists descended upon Okinawa to investigate the captured abyssal "ship", they unlocked a whole treasure trove of information and intelligence regarding what the Abyssals are and what objectives they have. To say that they hit the jackpot would be an understatement.

The Abyssals are a force comprised of seemingly human-looking beings, or rather artificial intelligences who then identify themselves according to ship classes. Their main goal is to disrupt all human nautical activity. To what end? We do not know. What we do know is that having analyzed the armor and armaments of this particular standard carrier, even though it looks like a lady with a staff and large, teethy headgear, we are able to develop weapons to counter the alien material.

But that's not all. The Abyssals operate on a gigantic hive-mind, and information is shared among all units of the Abyssal Fleet. This means not only do we know their whereabouts, we also know what their Artificial Intelligences are based off of. To our immense surprise, some very familiar names started popping up on the scientists' screens. Nagato. Enterprise. Bismarck. Hood. Aquila. Surcouf. Ships which had participated in the Second World War. Every ship has memories and mannerisms assigned to them, as are recommended armaments and equipments. We left nothing to chance, and downloaded everything we could. And not a moment too soon. A remote signal was transmitted to the Wo-Class' corpse, and it self-destructed, wrecking the naval warehouse in which it was stored in.

But we got what we wanted, and a whole lot more. Blueprints on how to construct our own anti-abyssal weapons were distributed to all major military powers, according to the ship's nationalities. When the USN unveiled the USS Enterprise after months of toiling, the public coined a new term for the new weapons of war.

Shipgirls.