[sinsofsolarempirefan]

Thats an old fashioned propeller right there. Must be quite noisy.

[naturalman1975]

Don't assume the propeller on the picture of the Collins is in anyway accurate. The RAN takes a lot of precautions over that particular piece of kit (this is no secret, or I wouldn't say it, of course - but the precise design itself is one they really do work hard to keep under wraps.

(Yes, the US knows what it is, because they helped design it - which is probably one reason why it's kept so secret - Americans understandably really don't like their allies leaking their secrets.)