Each Boomerang aircraft had three different identifiers…

Batch numbers
During construction, each aircraft was given a batch number, for the ordering of parts and materials. There were either 5, 10 or 20 aircraft in a production batch. Batch numbers consisted of a letter for each batch followed by a number for each aircraft in that batch (e.g. A1, A2, etc). The letters I, O and Q were not used as batch numbers, as they could be confused for numbers.

Usually a new contract (such as CA-1, CA-2, etc) started with batch “A”, but in the case of the Boomerang production this did not happen. Aircraft produced under the CA-12 contract started with batch “A”, under the CA-13 contract with batch “H” and under the CA-19 contract with batch “N”.

The definitive source for batch numbers is a ledger book filled out by Mr Gordon Parker, Supervisor in the Sales Department, and one of CAC’s earliest employees from 1936. This book is now held in the collection of the Australian National Aviation Museum at Moorabbin Airport. The list below has been transcribed from the Parker list, and also checked against photographic records and ID tags held in museums and private collections.

Batch numbers were usually taped to the firewall or the rudder (once the engine was mounted), and they are sometimes visible in factory photos.

Constructor’s numbers
These were a sequence of numbers allocated to each aircraft in the sequence that they came off the line. For example, Boomerangs delivered under the CA-12 contract were numbered from 824 to 928.

RAAF stores number
All equipment in the RAAF was allocated a stores number for tracking and accounting purposes. Aircraft were tracked under the category “A” and each aircraft was given a specific number, Boomerang aircraft being allocated the category A46.

Putting it all together
The photo below shows a Boomerang under construction. The batch number taped to the rudder is “D12-37”, this tells us the aircraft is the 12th aircraft in batch “D” (D12) and would be given the RAAF stores code A46-37. The aircraft was the 860th constructed by CAC (constructor’s number 860).
Photo from the Lewis Family Collection, State Library of South Australia (ref PRG 247/143/41).

The table below shows these numbers for all the CAC Bomerang aircraft, with batch numbers transcribed from Gordon Parker’s delivery records.

Caveat lector: These batch numbers were current at the time the aircraft left the factory. During RAAF service, various parts could be changed during repairs, resulting in possible differences between batch numbers and stores numbers as listed below. Also, the records kept by Gordon Parker are not infallible, there have been cases where errors have been found, so one should not expect that this historical list from the early 1940s will match with frames in existence today.

Note that constructor’s number 1054 (between batches “R” and “S”) was most likely allocated to the sole CA-15 prototype.

References:

Commonwealth Aircraft Corporation. Sales Department Aircraft Delivery Ledger; Kept by Gordon Parker. CAC Collection, Australian National Aviation Museum.

Commonwealth Aircraft Corporation. Aircraft Drawing Office Manual. Incorporating up to Amendment List No. 2, Melbourne, Australia, 1946.