Jim, very well stated on the issue of combining both the upset of capsized helicopter and the shock hazard of very cold water. I was skeptical of HEEDS when it first came out, in the USN, over 20 years ago, but a couple of my friends were in mishaps with HEEDS available and made me into a believer. It gives you those blessed extra seconds of not having to deal with "where the hell is my air?" while allowing one to deal with with "get out hand over hand before this thing takes me to the bottom!"