It was a routine patrol in the South Pacific for Topeka. Cruising between foreign ports with routine comms check in between, nothing unusual. Until it came.
It emerged from the depths with little warning. Topeka's radar spotted it first. It was huge, at least her size but the readings couldn't be correct. This thing wasn't man made, it was a biologic. A biologic headed straight for her.
Topeka opened her mouth, letting the water flow in and touch her sensitive receptors in the back of her throat as she inhaled the creatures scent. In an instant long dormant instincts reawakened and the submarine snarled, arming her torpedoes as she loaded them into the tubes.
"Topeka what's going on?" Her captain asked, touching the wheel only to have it spin suddenly and throw him off. He was thrown back and caught by a nearby crew member. "What's wrong?" He tried again, receiving a deep growl in response.
"Sir, I believe Topeka has gone feral." The crewman said.
"Nonsense!" The captain growled. "Topeka is a United States Submarine, why would she turn on us?"
"Maybe because there's something out there that's caused her to." The crewman replied.
Topeka's growling intensified and she let out a warning bark in her native tongue. This only served to incise the creature and it increased its speed towards the submarine. Topeka launched her torpedoes as it came into range but she never got the chance to know if they actually made their mark. The creature came in from the side, biting down on her hull. Topeka countered by guiding her torpedoes around towards it. They impacted and the shock wave tore Topeka's hull free from the creature's jaws, the teeth marks leaving a perfect imprint. The submarine rolled on her back, drifting. A bright light overcame her and then, darkness.
2 days later and 500 miles further south than she was supposed to be, she was discovered drifting amongst the ice of the Weddell Sea. Unconscious, half-frozen and barely alive...