Unless you believe George Orwell's claim that all art is propaganda; which, with all due respect to one of the twentieth century's finest minds, is poppycock. The propaganda film is a special kind of film, usually unbearable garbage. This one is an exception.
A German U-boat is sunk just off the coast of Canada and the surviving crew must make it through hostile enemy country to the neutral United States. After a short while their plight becomes known and the whole world is watching to see which nation, Canada or Germany, can manage to win the metaphorical battle.
The most interesting thing - considering the movie as propaganda - is that Powell's intended audience was the United States: he wanted to get that country involved in the war, or at least get the people of that country to support the war. Realise this and you realise how remarkably subtle the film is. Not once is Powell's goal explicitly stated or even alluded to; and even the underlying message (the USA *is* involved in the war, whether it wants to admit it or not) requires some thought to work out. Yet it's an integral part of the story. More explicit is the democracy vs. dictatorship theme, which is hammered home a number of different ways, not all of them obvious. (This theme is handled a bit too obviously now and then, I'll admit.)
Another interesting fact is that the hero of the story is either democracy, or Canada, or the Western Allies, or some such - no one person plays the role. The central characters are the Germans. In fact they're all quite likable (except for the doctrinaire Nazi, of course). Powell bends over backwards to inhibit anti-German sentiment. Despite all this we are not once on the Germans' side. We want them to be captured so long as they continue to serve an evil regime.
It's also a beautifully shot travelogue of Canada. And Ralph Vaughan Williams's score is lovely. He was seventy or so when he wrote it; he'd never written for the cinema before; he had his own ideas about what film music should be like.
