There is mention of John Sproule in a book I have at home called 'Hovering Angels' as I'm at work I don't have the ISBN etc but it's basically a history of the introduction of helicopters into the RN.
Funnily enough Lt Cdr Sproule's uniform (No 5s) was on ebay about a year ago, I had hoped the FAA Museum might have tried to buy it as he was an early pioneer of both helicopter flying and SAR techniques.
I was still using the 'Sproule Net' in the early 80's flying both Sea Kings and Wessex V, seem to remember it was quite tricky!!