I have no idea of the credibility of the site which is the source of the link I will put below, but it goes into a lot of detail regarding the CIA's involvement in the overthrow of Gough Whitlam's government.
I have always been suspicious of the CIA involvement because I was made aware of it, before the events actually happened.
I used to listen to parliament and political shows on the ABC, while working on site during the day, and a couple of weeks before the dismissal, a Labor pollie asked the Libs what they knew about the known CIA coup master, Marshall Green's activities in Australia, and why he was meeting with senior Liberals, including Sir Garfield Barwick?
I am no fan of nutty conspiracy theories, but I truly believe that there is a mountain of evidence regarding the most dramatic time in our political history, which we have never been allowed to examine, and so the questions remain.
http://www.american-buddha.com/cia.australia.htm