At the beginning of 1942, as it faced the prospect of numerous Japanese air raids, the Australian War Cabinet found it impossible to obtain sufficient numbers of operational, up-to-date fighter aircraft, in any form. At CAC, a light-weight "emergency fighter", which could be built quickly from scratch in Australia, was designed and a prototype built. As the CAC CA-13 Boomerang, it first flew in May 1942, and was rushed into full production.

It was acknowledged from the outset that the CA-13 was compromised by the only, low-powered engines then being manufactured in Australia. While Curtiss P-40 Kittyhawks were slowly becoming available to the RAAF, CAC became actively involved in three parallel solutions: upgrading the Boomerang when better engines became available (as the CA-14 and CA-19); local assembly, from components made elsewhere, of an already-proven fighter, and; development of an all-new replacement, with a full-sized airframe that was capable of mounting the largest class of aircraft engines then available (a project that later resulted in the CAC CA-15).
Local assembly of the P-51D (CA-17; Mk 20)
Plans to assemble a proven fighter locally began to bear fruit in December 1942, the War Cabinet began to make arrangements with North American Aviation (NAA) for CAC to assemble the P-51 Mustang. These arrangements were finalized in November 1943, with CAC scheduled to build 690 P-51Ds, from kits made in the United States by NAA.(As it awaited arrival of the kits, CAC privately continued work on the CA-15, as a possible back-up or even replacement for, the Mustang. However, the US-built radial engines intended for the CA-15 became unavailable, also hampering that project.)

Only 100 unassembled P-51s were ever delivered, and four reportedly had the "razorback" style canopy of the P-51B/C variant. In either late 1944 or early 1945, assembly of 80 of the P-51D kits commenced, under the designation CA-17 Mustang Mk 20 with Packard V-1710-3 Merlin engines, with the remainder being used for spare parts. The end of the war led to cancellation of the remainder of the kits ordered from NAA.
Local manufacturing of the CA-18 Mustang (Mk 21–23)
In late 1946, CAC received a contract to build 170 (later reduced to 120) Mustangs locally from scratch. These aircraft carried the new designation CA-18.

The first 40 were designated Mustang Mk 21 and powered by Packard V-1710-7 Merlins. 66 Mustang Mk 23s followed with British-built Rolls-Royce Merlin 66 or 70 engines.
A total of 14 Mustang Mk 22 reconnaissance aircraft were built with F24 cameras, and a further 14 were converted from Mk 21s.

Additional orders for the CA-18, as well as 250 two-seat variants, designated CA-21, were canceled in favor of further, US-built P-51D and P-51K variants.
Operational history
The first production CA-17 Mustang Mk 20, serial number A68-01 (not to be confused with the US-built prototype A68-1001), made its first flight on 29 April 1945 from Fishermans Bend. The aircraft was handed over to the RAAF on 4 June 1945 and was tested by the No. 1 Aircraft Performance Unit. Trials ended in October 1946, and the aircraft was placed in storage until 1953. Only 17 CA-17s were delivered to the RAAF by VJ-Day.

The first operational units to receive the CAC Mustang were No. 84 and No. 86 Squadron. Additional squadrons equipped with Mustangs (both American and locally-built) were No. 3, No. 4, No. 76, No. 77, and No. 82 Squadron as well as No. 21, No. 22, No. 23, No. 24, and No. 25 Squadron of the Citizen Air Force. The RAAF replaced its last Mustangs with de Havilland Vampires in 1959, while the last Mustang-equipped Citizen Air Force squadron, No. 24, retained its Mustangs until the CAF was disbanded in 1960.

Mustangs, No. 3 Squadron RAAF in Italy, 1944–45.
The unit’s Operations Record Book (ORB) contains the following entry for 17 November 1944: “Effective today, the squadron has been withdrawn from combat in order for pilots to receive training on Mustang aircraft”. On that day No. 3 Squadron RAAF became the first Australian unit to operate the fighter. Specifically, these were Mustang IIIs, or Mustang P-51C-1s and C-10s, and Mustang IVs (P-51K-1s, and later also K-5s and K-10s).

Training lasted until 21 November, and already on 22 November six aeroplanes, commanded by S/L Murray Percival Nash DSO, DFC and Bar, embarked on their first combat mission (denoted as a “Special Mission” in the ORB), during which they escorted a Lysander flying towards northern Italy. Tragically, the operation was cut short by Mustangs of the USAAF, which downed the Lysander before its escorts had a chance to intervene. The matter must have been serious, for it was to be the subject of a court martial. Over the next few weeks, weather permitting, the squadron performed reconnaissance flights, provided escort cover, or – as was most often the case – attacked ground targets in Italy and the Kingdom of Yugoslavia using 500-pound bombs. A closer reading of the unit’s ORB shows that whenever conditions allowed, the pilots flew two or even three missions a day. It is therefore clear that the Mustangs were actively used right until the end of the war. On 6 May 1945, the following was written down in the unit’s Operations Record Book: “The war has drawn to close in this theatre of military operations, and no further operational flights are required”. Two days later, on 8 May, the pilots of No. 3 Squadron celebrated Victory in Europe Day.

The Royal Australian Air Force’s (RAAF) involvement in the Korean War began on 25 June 1950 when No 77 Squadron was placed on standby for action. By November 1950, in addition to aerial operations, No 30 Communication Unit, No 491 (Maintenance) Squadron, and No 391 Base Squadron were attached to the United Nations Command and grouped into No 91 Wing, which was based in Iwakuni, Japan.

No 77 Squadron (77SQN) flew almost 19,000 sorties while in Korea – 3,872 in Mustangs .
Variants
CA-17 Mustang Mk 20
Aircraft built from kits supplied by NAA with V-1710-3 engines. 80 built.
CA-18 Mustang Mk 21
Locally-built aircraft with V-1710-7 engines. 40 built.
CA-18 Mustang Mk 22
Reconnaissance variant with F24 cameras. 14 newly built aircraft and 14 converted from Mk 21s.
CA-18 Mustang Mk 23
Variant with British Merlin 66 or 70 engines. 66 built.
CA-21 Mustang Mk 24
Two-seat variant of the CA-18. 250 ordered but not built.
Dart Mustang
Civilian modification of a CA-18 Mustang with a Rolls-Royce Dart turboprop engine. 1 modified from a Mustang Mk 22 but never flown in this configuration.
































(Text from Wikki)