That is really surprising for 1956. As a Catholic, I can recall being a teenager when some movies were banned because they uttered certain ‘words’!
I can imagine that film was either highly edited or even not shown in America at the time of its release. I saw yet another film a few weeks ago, “Age of Consent” with James Mason playing a middle-aged artist and a young Helen Mirren playing a late teen (although she was in her early 20s) set in Australia, filmed around 1968, and they couldn’t even show it in the U.S. at the time (even the opening credits were considered too risque for Columbia Pictures !). The film had liberal amounts of nudity from Miss Mirren (short of an open pubic shot). I’m not sure a “mainstream” film today could get an actress in a leading role to expose herself that much (especially when you consider there were no love scenes that involved her, just Mason and his soon-to-be real life wife in the film, very briefly).
I have to admit I’ve changed my opinion over the past decade as I’ve gotten older that I’d much rather see nudity in a film than extreme violence or gore. I don’t think the former can warp the public (especially youngsters) as much as the latter can. I guess I have more of a “European” mindset on that.