These are really hard to review. There are so many perspectives, so I'll talk about those.
Seeing the ships battle is always kinda weird because it's just the opposing ship members all yelling mumojumbo and numbers at eachother. So the 401 crew perspective is not my favourite.
I like seeing the mental models going about their lives. Seeing what's up with them. My favourite mental model is called Hyuna(?) I think? Something like that. The one with the black pompom pigtails.
We learn some more backstory of the characters and there's some much needed world building... Except it just kinda created more questions than it answered. Whatever. Reading this volume I wasn't sure if I really cared to pick up the next volume, but I still kinda do want to.
The mecha art continues to astound, but I think I'm just not too terribly interested in naval combat, or at least not in the way ARK PERFORMANCE write it (I can enjoy space-navies in Legend of Galactic Heroes). This volume shows an interesting change for the story, with bigger focus on the humanity of the Fog's mental models, while specifically bringing Takao closer to the main characters, allowing for more "generic" anime hijinks with her crush on Gunzou.
First, a main note of concern: this volume's cover features mental model Kirishima in a form not previously seen, as the big battle in the previous volume had her with a coat and shit. So I'm sitting over here thinking "damn, nice hips and little titties, I wonder who this character is, she looks like she might have a very nice 2D ass," but then I think I googled it some time ago (roughly a year transpired between -buying- this volume and actually -reading- it) and found it was the same chick from earlier. Kinda feel like it's the fault of the artstyle that I didn't realize the similarities between versions of the character (it's really only the lock of hair dangling in her face that made me understand lol). Somewhat funny as an extension, there's a bit of a twist later in this volume about one character looking like someone else, and I had to flip around to see how this new character -wasn't- actually just Iona....
So anyway, Haruna washes up near the home of a little girl who was genetically engineered to help Japan develop weapons to use against the Fog. Haruna senses something similar between herself and this girl, so she sticks around. The girl's creator/"father" realizes the issue of letting the Fog into his house, but is pleased to have found a "friend" for the girl. So Haruna, like Takao before her, is starting to gain a bit more overt a sense of Humanity.
Takao continues to be cute as fuck and/or really the most attractive character in the series (as we've not formally seen Kirishima in the clothes she wears on the cover). Actually, when Haruna is first seen in this volume, she's in nothing but lingerie, but she quickly retrieves her coat and tries to keep it on forever. I think her twintails are too thin-looking for my tastes (I appreciate volume at least on par with Tohsaka Rin from F/Sn), but they look good when she's disheveled and one of her pompom things is sliding down her hair. Hyuuga looks pretty good with her poofy hair and her quirky monocle, as well as her labcoat and pantyhose, but what's odd is I just googled her (to make sure I got her name right lol) and it seems the CG anime gives her bigger boobs than I recall from the manga. Odd. Still can't decide if I think Kongou is cute. The two Nagatos are cute, being the most explicitly Japanese-looking in their dress, which is surprisingly rare for series based on WWII ships (Azur Lane and Kantai Collection being the others I had in mind).
The fleet of fog ships have "mental models" (they look like girls), as does submarine 401. Volume 4 begins to tackle what they are and their role in the story. At this juncture, things are not clear. The story has evolved and is still interesting. I hope I regain my footing as I read on.
Despite the battles of ships and the cuteness of the mental models of the fog ships, this episodes unveils the issues usually found in the stories about artificial intelligences and of course the human factors that create the unpredictabilities that make a story interesting. Cool artworks too!