Queensland elects 10 senators to the Commonwealth Senate, having 6 year terms for each one, and with 5 senators due for re-election every 3 years. As it is called the "States' House", any casual vacancy during that six year term is filled, not by a special by-election, but by the Queensland State Parliament, an executive decision.
Senator Vince Gair, elected for a 1971-1977 term, was sounded out about becoming ambassador of Ireland, early in 1974. He had recently fallen out with his party, and resigned as president. A half-Senate election was due in May 1974, and normally he would not have been up for re-election.
But back then (not so now), the Act provided that an additional election writ be issued by the state at that first half-Senate election, if an extra resignation/vacancy occurred prior to those first five writs being issued. And the ALP planned to have an ALP candidate run in that sixth vacant spot in the May election who would be expected to win and thus boost the ALP numbers in the Senate (at that time on a knife-edge between Labour and Liberal).
Upon learning of Gough Whitlam's appointment of Vince Gair to Ireland, and of Ireland's acceptance of him, the race was on to issue the five writs in Brisbane early that same evening, so his formal resignation to the Senate President, expected the following day, could be followed by a Queensland State Parliament appointment (of a Liberal-National senator). A Liberal-National member in Canberra ensured Vince Gair formally voted in the Senate, later that evening, so the resignation could not be backdated to a time prior to that moment.
Click here for further details, including "The Dismissal". :-)
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