The African Queen(1951)

Charlie Allnut (Bogart) a hard-drinking riverboat captain runs a small boat, The African Queen, along the rivers of East Africa delivering mail and trading goods. 

He rescues Rose Sayer (Hepburn) afer invading WWI German troops destroy her mission, leading to her brother’s death.  Rose talks Charlie into an impossible patriotic journey down the Ulonga/Bora River so they can attack and sink the Louisa a German gunship that patrols a large lake.  Along the way they face “death a dozen times over” in the form of German marksmen, ravenous insects and life threatening rapids. 

Of course these two opposites finally attract and a sweet love story develops. 

After many difficulties, they reach the lake, sink the Louisa and swim off, happily ever after.