In 1942 the Royal Australian Air Force (RAAF) was looking for a new fighter aircraft. A team was put together and they traveled the world looking at current options. The contenders were the P-40, P-47, Spitfire, and the P-51 Mustang.

The final two were the Spitfire and the Mustang. The P-51 was faster, could fly farther than the Spitfire, and it was easier to build. The Spitfire could climb faster and out maneuver the Mustang. The decision was made. The P-51 Mustang would be Australia's new high altitude 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 30 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 British 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.
Imports from the U.S. began arriving in April 1945 and the last by September 1945.

After the Aussie Mustangs were surplussed, Australia became a popular site for P-51 airframes and parts. Restorers and collectors alike would travel down under to make deals and trades. Several P-51s have remained in Australia and are kept airworthy and well cared for by their pilots and owners.