I had fun reading some of the replies last time. So this time again. Some mcguffin thing appears or happens that makes boat girls real, but requires a human body that get's transformed. Females refuse to be turned into "fanservice sexdolls" and the military generally prefer males as they have combat experiences or at least made for war. Though for some odd reasons there is no real war anymore. There are exercise where combat girls fight against each other, but it's treated as a sport and as death matches.

Let's go with Azur Lane and the twist is that every boat girl has a limited amount of copies that could exist at any given moment in the world. So you gotta pick 3 prefered boat girls you want to be turned into. Or could be more or just say what body type of boat you would enjoy to be or not to be. https://azurlane.koumakan.jp/wiki/List_of_Ships_by_Image

You will also end up being put into a base where there is a commander and you feel inclined to follow his order, but not 100% submissive, unless he maxed out your affection gauge and put a ring on your finger. As last time, it won't completly rewrite your mind or your soul, but you might pick up traits from the boat girl you will become. Like as Unicorn you will end up refering to the commander as big brother. As Shinano you might end up falling asleep. As Kashino you may end up becoming more softie and also lactating. As Taihou you become a bit clingy etc.