A 1987 movie with the tagline: "The Beaches Have Become Battlefields... The Waves Are A War Zone!" so you know it's good.

Something interesting to note: In the USA it has an R rating. In Finland it's rated K-12, the equivalent of PG-13 (If I'm not mistaken). Then again, Friday the 13th is banned there, and a movie called "Sixtynine" is only rated K-16 (R equivalent) while it'd probably be NC-17 or even X in America. (IMDb categorizes it as 'Drama' though, so maybe it's not as sexual as I'm assuming from the title. :)