In 1942 the Royal Australian Air Force (RAAF) was looking for a new fighter aircraft. They decided on the P-51 Mustang as their high altitutde interceptor. In late 1943, an agreement between NAA and the RAAF was reached. An Australian aircraft company, Commonweath Aircraft Corporation (CAC), would build P-51Ds under license in Australia.

As part of the agreement, NAA would supply 100 P-51D Mustangs unassembled and Packard would supply some 80+ -3 Merlin engines. Delays mounted and the first CAC P-51 did not fly until April 1945. In all, 80 P-51s were completed from these parts and designated CA-17Mk.20, A68-1 to A68-80.

As the war came to an end, the total scratch built CAC P-51s was reduced to 120 aircraft. The CAC new built P-51s were designated CA-18. Versions would be the Mark 21, Mark 22, and Mark 23.

The Merlin V-1650-7 was used in the CA-18Mk.21 models. The CA-18Mk.23 use the Brittish built Rolls Royce Merlin 66 or 70 versions. The CA-18Mk.22 were modified like the F-6D reconnaissance versions. The last CA-18Mk.23 came off the production line in 1952.

Australia also received 298 P-51Ds from the U.S. under Lend-Lease. After the Aussie Mustangs were surplussed, Australia became a popular site for P-51 airframes and parts. Restorerers and collectors alike would travel down under to make deals and trades. Several P-51s have remained in Austalia and are kept airworthy and well cared for by their pilots and owners.