Movie buffs expecting to see a classic film about British military hero Adm. Horatio Nelson instead got a soft-porn flick about Nelson's love affair with an aristocrat. A spokeswoman for the Watershed Media Center said a mislabeled film container caused the mix-up Thursday night. The center planned to show ``Lady Hamilton,'' the 1941 film starring Vivian Leigh and Laurence Olivier that tells the story of Nelson and his love affair. Center spokeswoman Sara Davies said ``Emma Hamilton,'' the pornographic movie about the same subject, was mistakenly put in the film can. About half the audience of 20 walked out when shots of a half-naked woman appeared on screen. ``The film can was labeled `Lady Hamilton,' and we believe it was a catalog error by the National Film Archives,'' said Ms. Davies. ``The projection staff soon realized something was wrong and stopped the film.'' ``Lady Hamilton,'' also called ``That Hamilton Woman,'' was a U.S.-made film designed to increase pro-British sentiment during World War II. It was reportedly Winston Churchill's favorite movie. Ms. Davies said irate patrons received their money back along with a free ticket to another show. The center showed ``Streetcar Named Desire'' that night.