I have no idea what's in the manga, but just from the bits we've seen in the anime, it appears to me that Miho was in a tank that sunk underwater and she almost drowned. That caused her to decide not to do tankery and move to a different school, and may have given her a bit of a phobia about confined spaces. Just leaving tankery would be enough to make her family and former colleagues look down on her, I think.
As for the spying, I thought that was fairly low myself, but if this is really supposed to mimic war, then spying is probably somewhat okay -- like hacking the other side's communications.
The portrayal of Americans is in fact pretty nice, as
4Tran says. It's like a 1950s Japanese version of Americans: friendly and straightforward, enthusiastic, capable, and with overwhelming industrial production.
I just want to remind people that Alice, the American girl with reddish brown hair, is played by the long-lost Hirano Aya:
Full table of
character/seiyuu pics here.