The roar of engines and the thunderous gunfire echoed around the air.

The Battle of Midway was tipping in favor of the Eagle Union, scoring comfirmed kills against the Sakura Empire's fleet - four of which being her prized carriers. It seemed as though things would turn out alright for the Eagles.

However, three D3A 'Val' divebombers from the carrier Hiryuu were on their final attack approach as part of a last-minute act of revenge from her and her fallen comrades. All were heading for Yorktown. Her AA guns gave everything they had in their attempt to intercept the bandits.

"Ahh!"

Alas, all were in vain. The bombers scored hits on her, sending her body down to splash the surface of the water.

"Yorktown!" Various shipgirls cried out over the radio.

"Big Sis!" The one who said that was her younger sister Enterprise. Her tone became that of a heartbreak.

Despite the damage the bombs did to her, Yorktown was not out of the fight. She could afford to return back to the safety of the Eagle's frontlines by jettisoning non-essential equipment and making careful maneuvers.

"Hold on, Hammann's coming for you!" The reply from an Eagle destroyer attempting to help raised her spirits a little.

As she continued to lumber for home, her feet collapsed. Yorktown fell to the water, but - feeling determined - she got up again.

Suddenly, her vision began to blacken. Everything around her, including her hearing, was disappearing. Her strength was suddenly taken away as well.

"Big sister!" The faint voice of Hammann could be heard.

"Hammann…!"

XXXXXXX

"Mngh!"

Yorktown suddenly woke herself up and began panting. It appeared to her that she had experienced a nightmare about that fateful day.

"Ma'am!" A person quickly came for her while showing signs of relief. What got Yorktown's attention was her uniform. It was camouflaged in a myriad of marine camouflage colors. On the right of her uniform laid the name "O'Hara" - emblazoned in bright yellow. The left featured the letters "O.M.D.F." in the same color. "Are you alright?"

"Yes… It's just a nightmare…" The shipgirl answered. Coughing followed.

"Hold on, I have some water." O'Hara quickly provided her with a glass of warm water. Yorktown received it and took some sips.

"...Thank you." Feeling relaxed, the girl showed appreciation as she gave the glass back. The woman beside her felt the same.

Then, something hit Yorktown. She noticed that something was attached to her left hand. A long tube ran from it towards something beside her left. There, hanging from a metal stand was a bag containing clear fluids. But that was not all - upon closer inspection, she was not even wearing her usual uniform, only a medical gown.

Finally, the room where she was in - compared to the hospital back on her base, it was much more advanced, featuring various items not familiar to her. The only thing that she could identify was the familiar green canister for the storage of medical oxygen.

Whatever the case, Yorktown believed that she was rescued. But who or what fleet did that?

"Where am I?" A question was raised.

"You're on board the Osean aircraft carrier Altair for recovery."

"'Oh-see-an aircraft carrier?'" The shipgirl uttered with the first word being quite a mouthful.

"Correct. You were the only person on the water when we found you."

"I see..." Suddenly, Yorktown sensed that something was off. "Oh-see-an, Oh-sean, Oh-sean… I never heard of a country with that name before."

"Come again?" O'Hara requested.

"Where exactly am I?"

"The Atlantic Ocean." The woman answered.

"Atlantic?!" Yorktown could not belive what O'Hara answered. "That's impossible. I was at Midway, fighting the Sakura Empire before I took bomb hits. But how did I end up here?"

"Ma'am, you just need to calm down. We don't…"

"Do you have a map?" The request cut O'Hara short of her response. It was unusual for Yorktown to act quite desperate. "I just want to confirm for myself."

It took a moment for a reply to be aired.

"...Yes, we have. I'll bring them here."

"Thank you." Hoping to calm the girl's nerves, the older woman left to fetch a map.

All Yorktown could do was just wait within her bed. For her, time was passing slowly as O'Hara was unable to return with a map. Coughing returned for a moment, making Yorktown fetch the cup from the table to calm it down once again.

Finally, O'Hara returned with a map on hand. "Here you go. I have the map."

It was unrolled. What Yorktown saw shocked her to the core.

"Ah!?"

The map showcased the world, but unlike her familiar home, almost every area was wildly different in both size and shape - from the land to the sea. What was more, each contained the nations and their names. The most noticeable was the country with the name 'Osea.' This confirmed that she was on board a warship from that nation.

"So… I'm in another world...?" Tears began to form from her eyes.

O'Hara could finally figure out that she was not from her world just by looking and hearing what she said.

"I'm sorry..." She apologized and offered to comfort Yorktown.

With regret, the shipgirl started crying.

XXXXXXX

Sometime had passed.

Yorktown was fully recovered, but she had nowhere to go since she was in another world. The needle-attached tube on her hand was removed, replaced with a bandage to cover the spot. Due to the damage on her old clothes, she was given a replacement - a plain white t-shirt and a pair of pants featuring the same camouflage as O'Hara's uniform.

For the time being, she was redirected to one of the ship's quiet rooms where she would meet with the commander of the vessel.

"Yorktown, the commander of the ship would like to see you." O'Hara informed her, using the name of the shipgirl before turing around. "Sir, you may enter."

"Thank you, Lieutenant." An older male's voice responded.

The shipgirl turned her eyes to the doorway. There, she could a man in his late 50s entering. Unlike O'Hara, he was wearing the more traditional khaki uniform and a cap featuring the two terms "OFS Altair" and "CVN-41." Sandwiched in the middle was the impression of a ship resembling an aircraft carrier.

The door then closed. A private conversation was about to begin.

"Are you alright, ma'am?" A question from the man was aired.

"Yes. Yes, I am." Yorktown answered.

A brief pause was taken as the man took a seat beside her. "Look... I'm sorry if everything you know before is not here with you anymore. We just don't want you to suffer much longer when we saw you floating on the ocean. It's the least we could do."

Yorktown's emotional wounds slightly opened up upon hearing his words. "I appreciate your crew's efforts, sir. Right now, I really don't have anywhere else to go since I'm here."

"Speaking of which, Lieutenant O'Hara told me that you are from another world where a war was raging before you came here. Is that true?"

"That's correct. In my world, I come from the Eagle Union, a nation that values freedom and friendship among all else. We are part of the Azur Lane military alliance - dedicated to retaking our oceans from a mysterious enemy." She explained.

"A mysterious enemy?" The officer was intrigued.

"We call them the 'Sirens.' Their technology is unlike anything we have ever encountered. Well… to me and many others, I was born because of that."

The admission surprised the man. Fearing that something worrying could happen, he had some ideas.

"Uh, I think we should continue this at my cabin. I can't let everyone else onboard hear it." He stood up before beginning to lead Yorktown. "Follow me."

The girl agreed and stood up. For the first time, she could leave the perimeters of the medical bay.

Upon exiting the room, the sights changed. Covering the walls and ceilings of the hallways were lines of piping, each of which color-coded to their assigned purposes.

"By the way, I'm Theodore Steuben - captain of the Altair." He introduced himself.

"I'm Yorktown." The shipgirl followed.

"Just Yorktown? Last name?"

"I don't have a last name, to be honest."

Except for a few spots, the corridors remained narrow as they continued with their walk. They politely passed through numerous working men and women, most of which doing the same for their duties. Some even saluted out of respect upon seeing the captain passing by. They were even harboring questions regarding a girl with silver hair upon seeing her.

After a short while, they entered the captain's cabin. Everything inside was quite posh, as expected for captain's of most vessels. Decorated within the confines of the navy blue walls and white trim were numerous memorabilia - pictures, slogans, among others. On one part of the room laid a large flag encased in glass - featuring a two-tone desing of white over blue. On the foreground were six stars, three for each color. A smaller one was dotted near the white part's right star.

"Take a seat, Yorktown." Steuben offered.

"Thank you, sir." Yorktown replied as she continued looking around.

The shipgirl then caught something interesting on the sofa - on the white pillow was an aircraft carrier of some kind. Compared to those back on her world, it featured more angular shaping within the flight deck, and its island was placed further back within the stern. What was more intriguing was the lack of a visible smokestack. Painted on the bow was the hull number 41.

"The ship… I don't see a smokestack here."

"Coal here has been replaced by oil and other sources of energy, even on ships. Ours uses nuclear fuel to power everything." Steuben answered, causing Yorktown to wonder.

"'Nu-clear fuel?' What is that?"

"It undergoes a process called fission that splits its atoms into smaller ones, creating energy. The best thing is that it takes way longer for the ship to run out of them, giving us the ability to head for any part of the world without refuelling many times over." An easy-to-understand explanation was given.

"Amazing." Yorktown uttered. "How long do you think this would last?"

"Twenty years."

"That's a very long time. I wish I could have that ability."

"What did you say?" The captain asked upon hearing the last sentence.

"Sir, I wish I could have the ability to stay longer in the seas using that 'nuclear fuel.'" She reiterated.

"That stuff is dangerous if not properly contained. You would die of radiation poisoning." He then switched topics to the more important one. "Speaking of which, about you being a product of 'Siren' tech… I'm curious."

"Oh, right." The shipgirl remembered and took a seat. "Humanity discovered the potential of much of their technology and created us - shipgirls - to fight them."

"Shipgirls…?" Steuben responded in confusion. "So basically girls as warships - even using naval weaponry?"

"Yes. I am the lead aircraft carrier of the Yorktown-class. I also have younger sisters."

The captain was surprised to hear what Yorktown said. A girl who was the anthropomorphization of a ship sounds silly to untrained minds.

"Tell me this ain't real…" He returned to his prior composure. "You're serious?"

"I am serious." She replied. "That's the truth. Everyone knows about us, even the civilians."

With that, Steuben's mind was quite overloaded with words that required a lot of processing. Feeling stressed, his right hand was on the right side of his forehead.

"Did I offend you, sir?"

It took a while for the captain to regain much of his composure. "I'm fine. I couldn't exactly believe what you just said. You don't need to feel guilty about it."

Yorktown calmed down a bit.

"By the way... that rig you wore before we found you…"

XXXXXXX

After the talks, the captain guided her to the outside where she would witness the day-to-day operations of the Altair. It was almost evening, evident by the orange hues behind the clouds. What she did not expect was the myriad of planes on the huge flight deck.

Compared to all of her world's aircraft, every one of them on the ship was devoid of any propellers. Instead, a solid nose cone took their place. What was even more surprising to her were the openings in between the aircraft's pairs of fins - many have two of them while the rest have only one. They were even encased in dark metal.

"Are those even planes, sir?" Yorktown wondered.

"They're still planes, Yorktown." Steuben responded.

"Back in my world, our planes have propellers to make them fly. But those here don't have any."

"Well, propellers are replaced by jet engines. Even the civilian sector embraces it."

"How do they work, sir?"

"They work by compressing the incoming air and mixing it with fuel. Once ignited, the mixture is shot out from the back of the nozzles like that one over there." Steuben explained as he pointed at one with two rear openings. "You see those openings? That's where the mixture is shot out, creating thrust to move the plane forward. And compared to propellers, they fly way faster - even past the sound barrier."

The last sentence intrigued the girl. "Sound barrier? I thought that it could not be overcome."

"You just need an aerodynamic body and some good engines. Fly past that, the plane will experience sudden increase in aerodynamic drag and other effects. The important signs to comfirm it are that you will hear a boom unlike that of an explosive and you see puffs of white vapor forming around the plane."

"Theoretically, planes could arrive at the battlefield faster, yes?"

"Supposedly. Then again, most countries here field supersonic planes, so I would say fair game."

With that, Steuben turned his head to see the surroundings. On his left, he found something, a plane making an approach.

"Yorktown, look there to your left." The girl agreed and saw the incoming plane. She was filled with wonder.

"It's landing..." She uttered.

The plane descended from the sky. Its landing gear, flaps and arresting hook were deployed, and lights were tuned on for visibility. As it got closer, an unusual roar echoed around her, putting it in front of the other noises in the background.

Moments later, the plane touched down. Yorktown caught a glimpse of its greyish airframe and bubble canopy. She could even see the heat waves from the back of the plane. To her, what Steuben said was true.

"That plane… what is that?"

"That's an F-35 Lightning. Among the most advanced planes we currently field."

Yorktown felt like she could stay and continue looking.

(Somewhere in Osea - February 16, 2027)

In a large room, the installation's personnel were scanning for possible threats near and far - from the land to the sea. With various tools at their disposal, they were the eyes and ears of the Osean military and her allies.

As the day continued, something unexpected was caught by satellite. An unknown formation was growing east of the Atlantic Ocean. The person operating the computer began to call his superior.

"Sir, you might want to see this." His voice was heard by the officer, bringing him to the monitor

"What is it?" He asked before being directed to the screen. What he saw surprised him. "My God…"

With that, a new chapter began to unfold.