This film is the first, feature length, Japanese animated work (and coincidentally a propaganda film!) In an article written by Kevin Moist and Michael Bartholo, it is addressed that Miyazaki drew inspiration as a child from flying machines, quite the aviation fanatic. This is depicted in almost all of his films in some form or another, and three times in Howl’s Moving Castle. In his films, Miyazaki draws on the action of a flight scene to channel an excitement into his readers, possibly his own. Propaganda was certainly doing something similar, toward an almost opposed end of course; but aren’t the animals just adorable?
All of the film is available in pieces on YouTube if you have any further interest, there are some very familiar looking singing scenes and other animated mechanisms present.