African Queen

Humphrey Bogart and Katharine Hepburn star in this wonderful little story.
It is about their fight against a river and its perils as they try to battle the Germans during WW1.
The situation: the German troops just ruined her life as a missionary in Africa, and the local mailman on his mini barge is currently out of a job due to the war(fortunately his passion for drink softens his woes). Help could come, except that a powerful boat guards the lake and only passage for help to arrive. They find themselves helpless in the wilderness of Central Africa.
Their mission: they decide to try to fight their way downstream; past the enemy fortress, through reeds, mud, mosquitoes, crocodiles, waterfalls and rapids...and blow up the enemy ship.
Think the end is predictable? Not so much as you may think...