The Wikipedia take on the subject:
http://tinyurl.com/2f9uo8
As a young lad of six or so, to this day I recall the distinctive sound of Fairey Gannets (
http://tinyurl.com/yq6fog ) clawing their way in to the night sky at Changi, Singapore. I also remember asking Dad why such a small aeroplane could be so loud, and his reply about contra-rotating propellors. In true young lad fashion of course that would have lead to "why?" but I don't recall the rest of the conversation!