In Africa during WW1, a gin-swilling riverboat owner/captain is persuaded by a strait-laced missionary to use his boat to attack an enemy warship.
The African Queen (1952)
Director(s): John Huston
Producer(s): Sam Spiegel
Cast members: Humphrey Bogart, Katharine Hepburn, Robert Morley, Peter Bull
Studios used: Shepperton Studios
Filming facility: Woodlands and the River Ash
IMDB Link: http://www.imdb.com/title/tt0043265/