This may have been thrilling in 1916, but today it seems more of a curio. The Williamson brothers invented a camera to take pictures underwater, (the prologue tells us, complete with photos of them) so there's lots of shots of fish swimming, the bottom of the sea, men in diving suits and one battle with an octopus, which was a bit fuzzy. Still, the sense of watching movie history was strong, but don't expect too much in light of more modern techniques. What really bothered me was the hammy acting styles, with lots of arm motions and exaggerated facial features. It's the style that gave silent films a bad name. One who avoided this was Matt Moore, the hero of the film, and the only actor I recognized. Perhaps that is why he was still making movies in the 50's. The film uses plot elements of Verne's "The Mysterious Island" as well as "Twenty Thousand Leagues Under the Sea."