CAC Boomerang
The CAC Boomerang is a fighter aircraft designed and manufactured in Australia by the Commonwealth Aircraft Corporation between 1942 and 1945. 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. It was the first combat aircraft designed and constructed in Australia.
Different variants of the Boomerang were manufactured under a series of corresponding production contract numbers CA-12, CA-13, CA-14 and CA-19. The aircraft supplied under each contract incorporated modifications, typically aimed at improving the aircraft's performance. The Boomerang was handicapped by the available engine variant, which gave low power at altitude and resulted in the aircraft proving to be slower than contemporary fighter aircraft.
The Boomerang rarely engaged in aerial combat. 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 was commonly used for ground support duties, cooperating with Allied army units, in addition to secondary roles such as aerial reconnaissance and air sea rescue.
Development
Background
In the mid 1930s, some political leaders observed that both the Empire of Japan and Nazi Germany appeared to be preparing for war, which led to other countries commencing their own preparations.In Australia, the nation's small domestic aircraft industry required substantial expansion and reorganization to produce modern combat aircraft in sufficient numbers. While Tugan Aircraft had built eight examples of a small twin engine transport to their own design, as an organization they were too small to be reasonably expected to expand into the role of producing large numbers of modern combat aircraft in a timely manner. An additional hurdle was the lack of experience in Australia outside of light private and small commercial aircraft, as all military aircraft had been procured from overseas manufacturers, mainly in the United Kingdom. On 17 October 1936, with the encouragement of the Government of Australia, three companies formed a joint venture, registered as the Commonwealth Aircraft Corporation, which had the goal of developing a self-sufficient aircraft industry. Other companies joined them, and Tugan Aircraft was taken over by the CAC.
The CAC planned both engine and aircraft manufacturing and testing facilities at Fishermans Bend, Melbourne, purchasing tooling and equipment from manufacturers in both Britain and the United States. While the CAC 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 CAC later received substantial orders for large numbers of military aircraft, in particular fighters, to equip the Royal Australian Air Force. 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.
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 Australian squadrons were stationed in Europe, and four squadrons in Malaya. 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. There was a distinct need of a strong Australian fighter force at that time.
While most RAAF aircraft came from the UK, by 1942, the British aircraft industry was hard-pressed to even meet the needs of its own country. Meanwhile, companies in the United States possessed enormous aircraft manufacturing capacity, but their output was at this point being monopolized by the United States Army Air Forces and United States Navy, which were also at war with Japan. Even where capacity could be found for new aircraft to be built overseas, their delivery would require them to be shipped considerable distances in wartime conditions, with consequent delays and at the risk of considerable losses, in particular due to German U-boats and Japanese submarines.
While damaged USAAF fighters such as the Curtiss P-40 Kittyhawk and Bell P-39 Airacobra in Australia's region could be rebuilt by Australian workshops and even loaned to RAAF units, they were not available in sufficient numbers.
Origins
In late 1941, Lawrence Wackett, Manager and Chief Designer of CAC, began examining the possibility of designing and building a new domestically-designed fighter aircraft. The main challenge to this ambition was that fighter aircraft had never been manufactured in Australia. According to aviation author Rene J. Francillon, many experts considered that the licensed manufacture of a complete fighter aircraft would be beyond the capabilities of Australia's industry at that time. Wackett quickly decided to use elements of aircraft which were already being produced in Australia. 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.Overseas, the NA-16 had already become the basis of the North American NA-50 fighter, also known as the P-64, which had been used by the Peruvian Air Force in the 1941 Ecuadorian–Peruvian War. Crucially, CAC's licence to manufacture the Wirraway already contained a clause allowing the design to be modified. Wackett decided to use the airframe of the Wirraway as a starting point for the design of the new domestic fighter. This choice had the advantages of requiring little additional tooling, and of speeding up design and establishing manufacturing.
Although British designers had reworked the twin-engined Beaufort into a successful attack aircraft, the Beaufighter, this was not a suitable basis for the sought-after single-engine interceptor aircraft. Australian-made Beauforts used 1,200 horsepower Pratt & Whitney R-1830 Twin Wasp engines, which were made under licence at the CAC plant in Lidcombe, Sydney. Another factor in favour of the engine was that it was already in use to power the Grumman F4F Wildcat fighters of the United States Navy, which helped make the Twin Wasp a logical choice to power the domestic fighter design.
Wackett promptly recruited designer Fred David, an Austrian Jew who had recently arrived in Australia as a refugee. As David was technically an enemy alien, he had been interned by Australian immigration officials. He was well-suited to the CAC project, since he had previously worked for Heinkel in pre-Nazi Germany, and for Mitsubishi and Aichi in Japan. As a result of this past, David possessed an excellent understanding of advanced fighter designs, including the Mitsubishi A6M, used by the Imperial Japanese Naval Air Service, and the Heinkel He 112, a contemporary of the Messerschmitt Bf 109 used in small numbers by Axis air forces in Europe.
In December 1941, the management of CAC issued its authorisation to proceed with the detailed design of the new fighter aircraft. 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. It had a new single-seat cockpit with a sliding hood, and carried an armament of two 20 mm Hispano-Suiza HS.404 cannons and four.303 machine guns.
The proposal was presented to the Australian Government, which promptly gave its approval, viewing the CA-12 as appropriate insurance against the delay or cancellation of its order for US-built P-40 fighters, as well as a desire to maintain work at CAC. The ready availability of usable Wirraway components for the CA-12, which would greatly speed up any manufacturing program, was also viewed favourably.
On 18 February 1942, the Australian War Cabinet authorised an order for 105 CA-12 aircraft. Shortly after, the name Boomerang was selected for the aircraft. The ordering of production aircraft had been made in advance of any prototype being produced or maiden flight performed: the Boomerang had been effectively ordered 'off the drawing board'.
Prototypes and early production
On 29 May 1942, the prototype Boomerang, A46-1, conducted its maiden flight from Fishermans Bend, flown by CAC pilot Ken Frewin. This initial prototype had been completed within only three months of having received the order to proceed, which was a considerably rare accomplishment for the era. A46-1 was quickly put to use for a series of test flights, being flown either by Frewin or by RAAF pilot John Harper. These tests reportedly went smoothly, with the prototype proving to be easy to handle and quite manoeuvrable.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. On 15 July, No. 1 Aircraft Depot of the RAAF formally received A46-1 from CAC.
Comparison flight tests were undertaken by 1 AD, pitting the CA-12 against a Brewster Buffalo that had been lightened and re-weighted to approximate the flight characteristics of a Zero, as well as a Curtiss P-40E/Kittyhawk Mk I and a Bell P-400/Airacobra Mk Ia. It was found that the Boomerang was faster in level flight than the Buffalo, although the Buffalo out-manoeuvred it. The Boomerang was superior in armament, with two 20 mm cannon and four.303 calibre machine guns, all mounted in the short, thick wings. Its pilots were better protected, with generous armour plating, than Japanese fighter pilots.
While the CA-12 was lively at low level, its performance fell away rapidly above altitudes of 15,000 ft. Its maximum speed of 265 knots was not sufficient to make it an effective counter to Japanese fighters like the Zero and the Japanese Army's Nakajima Ki 43. Similarly, the best European fighters were reaching almost 350 knots, and even relatively sluggish contemporary fighters – like the Grumman F4F Wildcat and the Curtiss Kittyhawk Mk I – were substantially faster than the Boomerang.
From March 1942, there was less pressure to place the CA-12 into production as multiple USAAF units, operating a mixture of P-40 and P-39 fighters, were being deployed in strength to northern Australia. The RAAF had also begun to receive new Kittyhawk fighters. In June 1943, manufacturing work upon the original order for 105 CA-12s was completed. 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 were retrofitted onto early production models at operational bases as well.
In the face of difficulties experienced by CAC in the development of the CAC Woomera, a twin-engine bomber aircraft which was ultimately cancelled in September 1944, the Australian government elected to extend the production arrangement for the Boomerang, extending its orders from 105 to 250 aircraft. These additional 145 aircraft were manufactured in four distinct versions, the CA-13, the CA-14, CA-14A and CA-19. 95 CA-13s and 49 CA-19s, were completed. One prototype of the supercharged Boomerang CA-14 and its modified CA-14A form were produced. In February 1945, the final Boomerang to be manufactured, A46-249, a CA-19 model, was completed.