Love
Yes, it's a war film, and yes, it's an adventure film, but first and foremost The African Queen is a love story and the main theme throughout it is love. The love between Rose and Charlie is unexpected as they are far from being an obvious match - in fact, a hard-drinking sea dog and a prim teetotal English missionary are probably the opposite of compatible lovers. The theme of love throughout this film, though, is of unlikely love that turns quickly to a passion so deep that all else fades into the background. For example, the most sensible thing for Charlie to do would be to sail to safety and since Rose can't sail, to do this whether she likes it or not. He doesn't do this partly because her nagging breaks down his resolve but also because he can see what attaching the Louisa means to her. Very soon the two do not want to live without he other and both put the other's life ahead of their own; Charlie pretends he doesn't know Rose so that the Germans will punish him and spare her. Their love is so deep that they would rather die than live without the other and fortunately at the end of the movie it appears that they won't have to.
War
This is a war movie in that the part of Africa they are in has. Even colonized and is now being defended by the German army. The dangers come from the Germans and from Rose's patriotism that make her feel a responsibility to torpedo their ship. Although there is not battle action per se, the war nonetheless acts as the backdrop for the action and also provides the reason for the adventure that follows. Rose is determined to do what she sees as their duty and contribute to the war effort by killing the Germans on board the boat, which will also keep the African people safe from attack.
Alcoholism
Although Charlie is never actually designated as an alcoholic, his behaviors indicate that he is one. He drinks alone prior to meeting Rose. He drinks until he is comatose. He reacts badly to the loss of his drink supply when Rose pours it into the river. Bogart also plays him as a wizened captain who enjoys more than a drink or two on his travels. His behavior is that of an alcoholic and Rose is determined not to enable him, hence her pouring out what's left of the drink on board.
Patriotism
Rose, an Englishwoman, feels it her duty to avenge the death of her brother and also to attack the German target to play a role in the war effort. She patriotically slivers that any English person can outwit a boat full of Germans and this is not only something that they can do but something they are morally obliged to do as well. Although a successful attack would only take out that one boat it would also make the German's activities in the area more difficult which again would be beneficial for the long-term prospects of the British army in the war.
