RAAF Registration Number = RRN.
Army Registration number = ARN
Defence Registration Number = DRN
The Ronnie Raafies are still using the same Commonwealth registration number block they were provided in early 1942 by the Department of the Interior! (200000 +......). 'If it ain't broke, don't fix it'
Army 'moved on' in the early 1970s to the 5-digit series, which then progressed to the 6 digit 200000 + numbers, thereby 'reusing' numbers previously issued to RAAF vehicles.
Mike C