I've seen people bring this up as an interesting fact several times, but haven't seen any sort of sources. It's said that because fighter pilots were dying so frequently, they wanted to ensure their families would be taken care of if they died. The swinger's movement supposedly came out of this as pilots were expected to care for the families of fallen friends and group sex formed the necessary bonds to ensure this would happen. Is there any truth to this?
You're more or less right, but wrong war; Terry Gould's The Lifestyle: A Look At The Erotic Lives of Swingers ties everything back to WW2-Korean War era Air Force pilots and their wives popularizing the practice in America, with it really taking off in the 60's and 70's.
EDIT- I'll try and expand a little more on the contents of the text itself. It's been about 10 years since I've read it.
Gould uses the book as a way to deconstruct what swinging really is, and how it took off/evolved in America's post-WW2 landscape, up to today. Well, 1999...that's when it was published. He gives a decent history of how the movement evolved (ever wonder how key parties became a thing?), and how it still continues today, and goes on to make the claim that swingers tend to be (on average) far happier in their relationships than couples that don't engage in the activity. He has a lot of good number-crunching and data to illustrate this through statistics, and it can get a bit dry at times.
Another interesting topic he digs into is the demographics of swinging. The bulk of participants tend to be married, in their 30's-50's, have kids, and be more or less middle-class and up, usually educated, and usually fairly conservative on paper.
That's about as much as I can pull from memory and be confident in my explanation. I read it at the suggestion of a poly friend back in college.