Wikipedia lists Inspiration (1915) as the first film with non-pornographic nudity.
For films that were intended to be erotic or pornographic, you have to go at least back to 1896 for Le Coucher de la Mariée (or Bedtime for the Bride or The Bridegroom's Dilemma), where cabaret performer recreated her striptease act during a bath scene. The short film was released in the US in 1903.
There is more information in this Wikipedia article on nudity in film.
If you count the zoopraxiscope as 'silver screen' then this pushes the date back to at least 1883, with Eadweard Muybridge's studies for the University of Pennsylvania. These included Boys playing Leapfrog and Woman Walking Down Stairs. Of course (as you can tell from the names) these are hardly feature films, just several seconds of captured motion.
In Tarzen and his Mate in 1934 there was a swimming scene in which Jane was fully nude. It was not Maureen O'Sullivan who did the nude scene but an Olympic swimmer named Josephine McKim who swam in the same Olympics as Johnny Weissmuller did the nude scene. She was not only a beautiful woman but a superb swimmer as well having won 3 medals in the 1928 and 1932 Olympics. Maureen would not appear fully nude and the scene involved a lot of underwater swimming.