..... most have only served one term......
Indeed it seems that, if I have the count correct, at least 17 of the 27 Australian prime ministers to date were installed by their respective parties in periods between federal elections. So Gillard replacing Rudd is almost a mundane experience in an historical context.
Bruce became Australia's first prime minister without a general election being called.
Page became prime minister due to the death of a sitting leader and so he too never faced a general election as leader to get there. He gave way to Menzies who became prime minister without facing the people as head of the party (although he did stand for election as leader of the opposition the second time around).
Forde took the same route as Page.
Deakin, Watson,Reid, Barton, Fisher, Hughes, Menzies all resigned rather than be pushed by either their party or the House.
McEwan came to the prime ministership on the death of Holt. He was unmarried during his brief term as prime minister and also childless. He gave way to Gorton without a general election being called.
When it came to party room coups - Bruce rolled Hughes in Billy's incarnation as a conservative, McMahon rolled Gorton (à la Gillard and Rudd but with more blood on the carpets) and Keating rolled Hawke, to become prime ministers without going to the electorate for ersatz approval.
Neither Watson, Reid, Page, Fadden, Forde or McEwen went to a general election while holding the office of prime minister. McMahon's government lost the only time he went to the polls as PM.
Of the many who did not last long heading a federal government, the record for brevity must go to Forde who gave way to Chifley after eight days.
Whitlam was unique in that he was removed by the Governor-General using the reserve powers of the Crown.
Oh, and by the way - a total of six prime ministers have been born overseas. One of our most well-known prime ministers William 'Billy' Hughes was born in Wales just like the 27th Prime Minister Julia Gillard.