Possibly a 1918 gimmick to sell 'war bonds' -
14 March 1918: "Tanks will make their appearance in Sydney streets ... These are being constructed locally, and promise a realistic effect. The first salesman from the tank will be Sir Walter Davidson, the Governor of New South Wales."
https://trove.nla.gov.au/newspaper/article/92933811
Bit more detail of the bond sales 28 March 1918:
https://trove.nla.gov.au/newspaper/article/220494318
But what was underneath the models isn't stated. Although there is a reference elsewhere to them frightening horses!