Wo-Class is an Abyssal Class Aircraft Carrier from the popular Kantai Collection, she was only used by Erica Hartmann. As stated by Erica herself, the reason Erica wanted to become a ship is because she wanted to be stronger for both team Ilya and for Gilgamesh. The process of becoming a ship is by one of the Abyssal ships to drown the host to the bottom of the "Iron Forge" Where their soul/fate is tested to see if they're would make a good ship. Erica being except because of her past performances turned into the Abyssal Aircraft Carrier Wo-Class.
Erica later on had decided that enough was enough and that more people wanted Erica as a person rather than the Wo-Class who had held Erica's soul inside of them to be able to be in this realm of existence with a delicate surgery by Ilya she was able to return to her body. Wo-Class is no longer being used and their whereabouts are currently unknown.