9. Achievements (contd.):
OK, I think now I got it. The achievements are accumulated and show everything you have achieved in any campaign ever. Strange, though, that
Magazin Explosion is still gray although I'm 100% sure to have sunk a lot of ships by hitting the magazine.
Also it is sometimes very difficult to scroll the achievements; the list is awfully sticky then. Maybe this related to the bomber action tap problem (1., above)?
Anyway, there are more important features than the achievements ...