In "The African Queen", who or what was the African Queen?

The African Queen is a 1951 British-American adventure film adapted from the 1935 novel of the same name by C. S. Forester. The film was directed by John Huston and produced by Sam Spiegel and John Woolf. The screenplay was adapted by James Agee, John Huston, John Collier and Peter Viertel. It was photographed in Technicolor by Jack Cardiff and had a music score by Allan Gray. The film stars Humphrey Bogart (who won the Academy Award for Best Actor – his only Oscar), and Katharine Hepburn with Robert Morley, Peter Bull, Walter Gotell, Richard Marner and Theodore Bikel.

In the story, the African Queen is a steam-powered launch, owned by a Belgian mining corporation, that plies the upper reaches of the Ulanga River.

The African Queen was selected for preservation in the United States National Film Registry in 1994, with the Library of Congress deeming it "culturally, historically or aesthetically significant". The film holds a 98% rating on Rotten Tomatoes, based on 41 reviews.