Aoki Hagane is a good anime. It looks really nice (in my opinion, although I know that the CG style is not everyone's favourite, it's easy on the eyes and I personally enjoy the art quite a lot) and it has plenty of amazing moments (no spoilers, of course).
I won't write a detailed summary of the story, but I will say that the story line of Aoki Hagane is not exactly new - mysterious non-human battleships overpowering all of mankind, except for Chihaya Gunzou and the rest of the crew of the Fog submarine I-401, Iona, who are attempting to cross the Pacific in one last attempt to save humanity. It's not a huge leap from, to name an anime at random, Strike Witches, especially with the common idea of certain individuals of the Fog joining the heroes.
The actual story itself is fairly simple, but generally remains sensible and within the bounds of its own rules (outside of a few plot holes which only arise in hindsight). Instead, the anime tends to focus more on the Fog and their interactions. This isn't necessarily a bad thing as the Fog (the 'mental models' of the enemy warships) are interesting enough characters by themselves. Even so, the ships are quite obviously the main characters of the anime, bar a handful of episodes which show the human politics which are going on in the background.
By and large, however, the humans - and most noticeably, Iona's crew - take a backseat to the other characters. We are barely given a few seconds in the first episode which hint that Gunzou may actually have a backstory, but not even the slightest attempt is made to explore this - and even less so for the other members of his crew, most of whom have less lines than a certain teddy bear. This is a shame, because initially I had the impression that Aoki Hagane was going to be an anime about Gunzou rebelling against the government as much as it was about fighting the Fog.
Putting aside the fact that Gunzou and his crew have badly (if at all) explained motivation for their part in the story, I feel that Aoki Hagane does a good job of building those characters which it chooses to build. The ships are distinctive and it's interesting to watch their characters grow over the course of their dialogues.
So, in summary: Aoki Hagane is a very good anime, that gives a new meaning to the phrase 'nice boat'. There are many things which it does well, as well as things that it does not do so well. Personally, I find this anime is very enjoyable in spite of the main drawback (which is the lack of character building for any of the human characters), but I can see how it would simply be far too irritating to have so many unanswered questions. So, I will give this anime a tentative 8, because I feel that what it does do is done very well.
