Approved for production shortly following the Empire of Japan's entry into the Second World War, the Boomerang was rapidly designed as to meet the urgent demands for fighter aircraft to equip the Royal Australian Air Force (RAAF).

During early wartime operations, the Boomerang was mainly dispatched to equip home-based squadrons, freeing up other fighters for use overseas.

In later service, the Boomerang would commonly be used for ground support duties, cooperating with Allied army units, in addition to secondary roles such as aerial reconnaissance and air sea rescue.

[3] While the company initially pursued the development and production of the CAC Wirraway, a single-engine armed advanced trainer aircraft which was a licence-built version of the North American NA-16, the firm later received substantial orders for large numbers of military aircraft, in particular fighters, to equip the Royal Australian Air Force (RAAF).

[3] In July 1940, when the United Kingdom was the sole European nation still fighting against Germany, the Australian Government issued a statement advising that "from this date onward Australia can rely on England for no further supplies of any aircraft materials or equipment of any kind.

[3] On 7 December 1941, the Pacific War began with a series of unanticipated near-simultaneous attacks by Japanese forces against Pearl Harbor, Thailand, Malaya and the Philippines.

With Japan gaining control over vast areas of the Pacific and South East Asia within just a few months, Australia was in a precarious position.

Two of the Malayan squadrons were equipped with Lockheed Hudson medium bombers, one with Wirraways as general purpose aircraft, and another with the lacklustre Brewster Buffalo fighter.

[3] While USAAF fighters such as the Curtiss P-40 Kittyhawk and Bell P-39 Airacobra that were being used in the region that were damaged during service could be rebuilt by Australian workshops and even loaned to RAAF units, they were not available in sufficient numbers.

Only two military aircraft were in production at the time: the CAC Wirraway, based on the North American NA-16, and the Bristol Beaufort bomber.

However, Australian-made Beauforts used 1,200 horsepower (890 kW) Pratt & Whitney R-1830 Twin Wasp engines, which were made under licence at the CAC plant in Lidcombe, Sydney.

[5] Wackett promptly recruited designer Fred David, an Austrian Jew who had recently arrived in Australia as a refugee.

[5] The aircraft, which had received the internal designation of CA-12, used the wing, tail assembly, undercarriage, and center section of the Wirraway in combination with a new forward fuselage, which housed the larger Twin Wasp engine.

On 29 May 1942, the prototype Boomerang, A46-1, conducted its maiden flight from Fishermans Bend, flown by CAC pilot Ken Frewin.

[10] An issue with engine cooling was encountered, which led to a revision of the oil cooler intake and the addition of a spinner to the propeller upon A46-3 onwards.

[12] During production of this batch, several modifications and improvements were incorporated onto the CA-12, these included the strengthening of the spinner back plates and belly tank locating pins, the installation of underwing night flying identification lights, and a revised electrical starter system; many of these modifications would be retrofitted onto early production models at operational bases as well.

The Wright engines ordered were not delivered as scheduled, and in mid-1942 Wackett authorised use of the 1,850 hp (1,380 kW) Pratt & Whitney R-2800, which was available from the CAC factory in Lidcombe.

CAC eventually returned to the Twin Wasp, to which it added a General Electric B-2 turbo-supercharger mounted inside the rear part of the fuselage, new propeller gear, a geared cooling fan (influenced by intelligence reports from Europe regarding captured German BMW 801 twin-row radial engines, which were used by the Focke-Wulf Fw 190A) and a larger, squared-off tailfin and rudder.

It had a stubby appearance, due to the smaller Wirraway airframe being paired with the considerably larger 1,200 horsepower (890 kW) Pratt & Whitney R-1830 Twin Wasp radial engine, which drove a three-bladed Hamilton Standard Hydromatic propeller, license-built by de Havilland.

[9] The wing used a single spar and a stressed skin construction, along with fabric-covered ailerons, aluminium trim tabs and split trailing edge flaps.

[12] The Boomerang had a new single-seat cockpit directly over the centre of the wing, which was furnished with a sliding canopy with 1.5-inch (38 mm) bulletproof glass and armor protection.

[12] Common to many of the latest fighters at the time, the Boomerang was equipped with automatic cannons; as no such weapons had previously been manufactured in Australia, a pair of British-made Hispano-Suiza 20 mm were used.

[citation needed] Other armament fitted included four Browning .303 machine guns, with provision for up to four 20 lb smoke bombs; all of these were mounted within the wings.

[18] On the evening of 20 May 1943, Flight Lieutenant Roy Goon became the first Boomerang pilot to scramble on the Australian mainland against Japanese bombers.

[18] In this vital mission, the Boomerang directly contributed to the extensive ground war in the jungles of the South West Pacific theatre, which was often characterised by widely dispersed, small unit actions, which typically fought at close quarters and with uncertain front lines.

In addition to strafing Japanese ground forces with cannon and machine gun fire, Boomerangs often dropped smoke bombs to mark targets for other units to attack.

Some of the aircraft were shot down, including two from friendly fire by US forces, and many were damaged during accidents while landing, often because the Boomerang was prone to ground looping.

In this role, the Boomerang would get in close to confirm the identity of the target and mark it with a 20 lb (9 kg) smoke bomb, with the bomber then delivering the major ordnance from a safer distance.