Australian Dept of Defence D/l\D on the receiver

[Kiwi]

Not sure of that logic, 9mm was not a common round outside Europe. Japanese did not use it.
Other than the Sten, the British did not use it. The Sten was because they were for use by Resistance and the 9mm WAS the available round in Europe.
More like a capture from WWI when Australia annexed New Guinea to deny German raiders a base.
Look up the SMS Emden