BBadanov
I think there might have been some confusion with your statement "the Australian Army hasn't operated the Chinook since 1973" - which could be (mis)read to mean "Australia hasn't operated Chinooks".
As for the 1973, ... Wikipedia says (at
No. 12 Squadron RAAF - Wikipedia, the free encyclopedia) 12 Sqn reformed in 1973 with the Chinooks being delivered in 1974.
Reports other than the ABC also refer to 1973 - perhaps derived from Defence web site
RAAF Museum: RAAF Aircraft Series 3 A15 Chinook which says they were accepted by Defence in October 1973. Operational no doubt came some time later.
cheers
layman