This was one of the manga I got from a Loot Anime crate that I finally cracked open.
After the sea level rises, a fleet of ships dubbed the Fleet of Fog took control over the seas, keeping humanity from traveling between continents or islands. A weapon has been developed to fight them and the crew of the sub I-401 is tasked with getting the prototype from Japan to America but the route takes them right through the Fleet of Fog.
So, there’s this motley crew, secret weapon, and of course the ships have a humanoid avatar that’s a cute girl. I had to trudge through this because it felt like a diluted Outlaw Star/Blue Sub Six mashup that made me wish I was watching those instead. I can’t even give it a proper rating because I didn’t finish it. I won’t be reading any more of this series and I gave away the volume I had.