The Secret of the Submarine was released on May 22, 1916
Two of the episodes of this 15-part adventure serial were filmed on California's Santa Cruz Island by the "Flying A" film company.
"Some unusual stunts were done at Santa Cruz Island for The Secret of the Submarine, and still photos secured by Faxon Dean are exceptional. One shows the house on the cliff after it had been dynamited. It was caught toppling down the cliff-side. Another shows Al Thompson making a leap over a precipice sixty-five feet high. This was not a regular dive. Thompson struck the water below but was unhurt." – Morning Press (Santa Barbara, California), April 26, 1916
The plot involves a young woman, whose father has invented an apparatus that enables submarines to dive to a great depth. She battles foreign spies who are trying to steal the secret plans of the apparatus.
(Submarines were in the news during World War I, so this was a very timely serial. The United States had not entered the war yet, but there was much talk about "preparedness.")