Kinky!
It always bothered me that there was this 50s love triangle going on in this movie but that the men didn't seem too competitive or angry with each other about it. Normally in this kind of situation you see some kind of fight or argument at some point in the movie. Weird. Then later on one of them rescues the other one when he really didn't have to and they have a nice underwater male bonding moment. Neat. Then later all three of them are around a table in a club having a great old time and...
and...
oh, good lord, they're gonna have a threesome aren't they? That's why they didn't fight earlier, all three recognized each other for what they were: swingers. And with the submariner always out to sea and unable to settle down it's a perfect solution for all of them.
So I just want to commend It Came From Beneath The Sea for being able to go go beneath the film censors' radar and fairly portray alternative lifestyles in the 1950s.