Queen of the Sea (1918)

Annette Kellerman, the Australian swimming star of the early 1900s, made a number of films, most of them in the 1910s, which displayed her athletic skills. Most of these films were underwater fantasies, and this one was no exception. Here, Kellerman is Merilla, a mermaid who is the "Queen of the Sea." Not satisfied with being a mermaid, she wants a mortal human body with an immortal soul. She discovers she can achieve this if she saves four human lives. King Boreas, master of storms (Walter Law), is wrecking ships left and right so his daughters, the Sirens, can drown the sailors. Merilla sees this as a prime opportunity to save some lives and rescues three sailors. Boreas, however, captures her and locks her up. She is rescued by the appropriately named Prince Hero (Hugh Thompson), and in revenge Boreas overturns his bark. Merilla saves him and Boreas then imprisons Hero's betrothed, Princess Leandra (Mildred Keats). Merilla rescues her, too, but the princess realizes that Hero and Merilla -- who has earned her human stripes -- love each other, so she is willing to let him go.