CAC Boomerang

The CAC Boomerang was a World War II fighter aircraft designed and manufactured in Australia between 1942 and 1945. The Commonwealth Aircraft Corporation produced Boomerangs under the production contract numbers CA-12, CA-13, CA-14 and CA-19, with aircraft supplied under each subsequent contract incorporating modifications and improvements. The Boomerang is significant as the first combat aircraft designed and built in Australia.

Background
The Pacific War began on 7 December 1941 with surprise attacks by the Empire of Japan on Pearl Harbor, Thailand, Malaya, and the Philippines. Within a few months, Japanese forces had conquered vast areas of the Pacific and South East Asia. During these campaigns, the ill-prepared Allied air forces in the Pacific suffered devastating losses.

Because of political and cultural ties between the United Kingdom and Australia, British manufacturers were the main source of RAAF aircraft. However, the British aircraft industry had long been hard-pressed to meet the needs of the RAF. Although United States companies had enormous aircraft manufacturing capacity, their output was destined for US air units. When new aircraft built overseas did become available, they would be shipped long distances in wartime conditions, with consequent delays and losses. While USAAF fighters damaged during service in Australia, such as the Curtiss Kittyhawk (P-40) and Bell Airacobra (P-39/P-400), could be rebuilt by Australian workshops and loaned to RAAF units they were not available in sufficient numbers either.

CAC examined the possibility of designing and building fighters. The main challenge was the fact that fighter aircraft had never been built in Australia. Only two military aircraft were in production at the time: the Bristol Beaufort twin-engined bomber and the CAC Wirraway, a single-engine armed trainer/ground attack aircraft, based on the North American Harvard. While the Beaufort was not a suitable basis for a single-engine fighter, its 1,200 horsepower (890 kW) Pratt & Whitney Twin Wasp engines were made under license at the CAC plant in Lidcombe, Sydney and also powered the Grumman Wildcat fighters used by the U.S. Navy. Consequently, the Twin Wasp was a logical choice for a stop-gap fighter design. The Harvard had already become the basis of the North American NA-50 (P-64) fighter (which had already seen action with the Peruvian Air Force). The Wirraway likewise provided a starting point for the Boomerang's airframe.

Like the latest fighters at the time, planning for the Boomerang included automatic cannons. As no such weapons were manufactured locally, a British-made Hispano-Suiza 20 mm which an Australian airman had collected as a souvenir in the Middle East was reverse engineered.

Development


Lawrence Wackett, general manager and former chief designer of CAC, recruited designer Fred David, an Austrian Jew who had recently arrived in Australia as a refugee. As David was technically an enemy alien, he was interned by Australian immigration officials. He was well-suited to the CAC project, since he had previously worked for Heinkel in pre-Nazi Germany, as well as Mitsubishi and Aichi in Japan. As a result, David had an excellent understanding of advanced fighter designs, including the Mitsubishi A6M ("Zero") (used by the Imperial Japanese Naval Air Service) and the Heinkel He 112 (a contemporary of the Messerschmitt Bf 109 and used in small numbers by Axis air forces in Europe). Design work began on 21 December 1941, at the CAC factory in Fishermans Bend, Melbourne.

The Boomerang was a small fighter, designed with an emphasis on manoeuvrability. It had an overall length of just 7.7 metres (25.5 ft) and an 11 m (36 ft) wingspan. Although the original intention had been to use as many Wirraway components as possible, the final design was quite different, with shorter wings, a shorter, wood-sheathed, aluminium-framed fuselage, increased strength for combat stresses and a new centre section.

On 2 February 1942, before the debut flight of the Boomerang's prototype, the RAAF ordered 105 CA-12 (Mark I) variants. The prototype commenced test flights on 29 May, with pilots Ken Frewin (CAC) and John Harper (RAAF). On 15 July, No. 1 Aircraft Depot RAAF received A46-1 (bu. no. 824) from CAC. Comparison flight tests were undertaken by 1 AD, against a Brewster Buffalo (A51-6) that had been lightened and re-weighted to approximate the flight characteristics of a Zero, as well as a P-40E (A29-129) and a P-400 (BW127). It was found that the Boomerang was faster in level flight than the "Zero", although the Buffalo out-manoeuvred it. The Boomerang was superior in armament, with two 20 mm cannon and four .303 calibre (7.7 mm) 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 (4,600 m), and its maximum speed of 265 knots (490 km/h) was not sufficient to make it an effective counter to Japanese fighters like the Zero and the Imperial Japanese Army Air Force's Nakajima Ki 43 ("Oscar"). Similarly, the best European fighters were reaching almost 350 knots (650 km/h), and even relatively sluggish fighters like the Wildcat and the Kittyhawk (which would become the main fighter used by the RAAF during the war) were much faster than the Boomerang.

As test and trial flights commenced, CAC had already begun work on a new variant, the CA-14, to address the Boomerang's deficiencies in speed, climb and ceiling. The CA-14 was designed around an order for 145 U.S.-built, 1,700 hp (1,268 kW) Wright Cyclone R-2600 engines. However, 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. However, the significantly greater weight of this powerplant led to an unacceptable risk of undercarriage failure. (The R-2800 engine would later be the basis of design work on the Boomerang's successor, the CAC CA-15, also known as the "Kangaroo".) 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 propellor 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. By July 1943, the significantly re-worked CA-14 prototype, now known as the CA-14A, had a top speed which was 25–30% better than the CA-12, and an operational ceiling which was 4,000 ft (1,200 m) higher.

Testing of later Boomerang variants found that they compared favourably with the Spitfire Mk V and early Thunderbolts and Mustangs. By this time, however, British-built Spitfires had filled the interceptor role and Mustangs had been ordered, to fill the bomber escort, air superiority and close air support roles. Consequently, production Boomerangs were never fitted with superchargers.

Operational history


Boomerangs that reached RAAF training and frontline units were delivered under three different CAC production contract numbers: CA-12, CA-13 and CA-19, incorporating various minor improvements and modifications. A total of 250 aircraft of these marques were built: 105 CA-12s, 95 CA-13s and 49 CA-19s. The CA-13 and CA-19 are sometimes known collectively as the Boomerang Mark II.

On 19 October 1942, CA-12 A46-6 (bu. no. 829) became the first Boomerang to reach a training/conversion unit, when it was transferred to No. 2 OTU, from 1 AD. No. 83 Squadron (83 Sqn) became the first fighter unit to receive Boomerangs, when several were delivered to it – replacing Airacobras – at Strathpine Airfield, in Strathpine, Queensland, on 10 April 1943. A few weeks afterward, CA-12s were also received by a frontline air defence unit, No. 84 Squadron which was stationed on Horn Island Airfield, in Torres Strait. The third Boomerang fighter unit, No. 85 Squadron – like 83 Sqn – was performing home defence duties, at RAAF Guildford (known later as Perth Airport); the Boomerangs replaced the squadron's Buffaloes.

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. Goon, part of an 85 Sqn detachment at RAAF Learmonth, near Exmouth, Western Australia, undertaking air defence of the Allied naval base  at Exmouth Gulf (codenamed "Potshot"), took off to intercept Japanese bombers. After Goon had sighted them, the bombers dropped their payloads wide of their target and left the area.

84 Sqn had been deployed to Horn Island – a US Army Air Forces bomber base – in an attempt to address Japanese air raids and the continuing shortage of fighters in this area. The squadron was only modestly successful however. The Boomerang's low top speed and poor high altitude performance meant that No. 84 could drive off enemy attacks but rarely get close enough to Japanese aircraft to bring their guns to bear. On the only occasion that a Boomerang did close on a Japanese aircraft, its guns jammed. There were not many air raids in this area, and after using Boomerangs for eight months No. 84 Sqn upgraded to the Kittyhawk.

The Boomerang found its niche as a light ground attack aircraft, a vital role as the ground war in the jungles of the South West Pacific theatre was often characterised by widely dispersed, small unit actions, fought at close quarters, with uncertain front lines. The Boomerang was ideal in this role because it: had the range to go wherever it was needed when it was based close to ground operations; had heavy armament; was agile and easy to fly, meaning that pilots could get close to ground targets, avoid ground fire and rough terrain and; featured extensive armour plating and a wood and aluminium airframe, that could withstand significant battle damage. Some of the aircraft were shot down, including two accidental "kills" by US forces, and many were damaged during accidents while landing, often because the Boomerang was prone to ground looping.

No. 4 Squadron and No. 5 Squadron flew Boomerangs in New Guinea, the Solomon Islands Campaign and Borneo Campaign, also in the close support role, with marked success. Flying in pairs (one to observe the ground, the other to observe the air around them), their tasks included bombing, strafing, close infantry support and artillery spotting. When attacking larger enemy formations Boomerangs often operated in conjunction with larger aircraft. 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 "cooperating" aircraft delivering the major ordnance from a safer distance. A partnership between 5 Sqn Boomerangs and Royal New Zealand Air Force Corsair fighter bombers during the Bougainville Campaign was said to be particularly effective.

No. 8 Communications Unit used Boomerangs to assist with air sea rescue operations in New Guinea.

The sole CA-14A was used for research by No. 1 Aircraft Performance Unit RAAF, and was also seconded to the Bureau of Meteorology for a period after the war ended.

Variants

 * CA-12 (Mark I)
 * The first single-seat fighter version, 105 built.


 * CA-13 (Mark II)
 * Improved version of the CA-12, 95 built.


 * CA-14
 * One aircraft fitted with a turbo-supercharged engine, did not enter production. Serial number A46-1001.


 * CA-14A
 * The CA-14 prototype was later modified to have a square tail and rudder


 * CA-19
 * Tactical reconnaissance variant with a single vertical camera in the fuselage, 49 built. Serial numbers: A46-201 to A46-249.

Operators

 * Royal Australian Air Force
 * No. 2 Operational Training Unit (October 1942–1945)
 * No. 4 Squadron (August 1943 – August 1945). Code letters: QE
 * No. 5 Squadron (November 1943 – August 1946). Code letters: BF
 * No. 83 Squadron (September 1943 – August 1945). Code letters: MH
 * No. 84 Squadron (April 1943 – October 1943). Code letters: LB
 * No. 85 Squadron (May 1943 – January 1945). Code letters: SH
 * No. 8 Communications Unit (February 1944 – August 1944). Code letters: ZA
 * No. 8 Communications Unit (February 1944 – August 1944). Code letters: ZA

Survivors


Three Boomerangs remain airworthy today, all in Australia:
 * A46-122 CA-13 "Suzy Q" (VH-MHR) with the Temora Aviation Museum


 * A46-206 CA-19 "Milingimbi Ghost" which was formerly with Lynette Zuccoli at Toowoomba, Queensland until donated to the Museum of Australian Army Flying at the Army Aviation base located at the nearby town of Oakey is now on static display.


 * A46-63 a CA-12 from 1943 first flew again on 26 June 2009 as VH-XBL. The restoration includes the provision of a passenger seat.

A full-scale, airworthy replica with many original parts is based in the United States. Several others are under restoration to fly in both Australia and the USA. This includes A46-90 which is currently being restored to airworthy status.