My recollection from the late 70s was, following a fast jet ejection into a very stormy North Sea, the helicopter winchman died attempting the rescue. The F4 at that time had a 35 kt crosswind limit. Someone (can't remember who) was tasked with finding out what limits, if any, other air forces who flew over the North Sea in winter applied. The answer was around 35kts. This coincided with the crosswind limit and so, as I recall, this was adopted by 11 Gp as a reasonable working limit. Incidentally, the limit for wearing immersion suits was 10C. Having since done quite a bit of scuba diving and spent some time in the sea at 10C or so, that limit is mighty low. I believe the RN used 15C and that seems to me to be much more sensible.