I think in the movie is a scientist which recruits a young boy who lost his home and probably family as well (to a fire?). This young boy advances to the rank of a cadet in the movie. The scientist’s daughter gets kidnapped by the evil airship (which is controlled by itself like an AI and not by a person if I remember correctly). The plot twist in the movie is that the boy finds out that the evil airship was build by the scientist himself.
Also, I remember a scene where the recruits board a pirate ship and loot for supplies.
Many thanks in advance for any clues!