In early 1939, the Australian Government ordered large numbers of Bristol Beaufort bombers, to be built in railway workshops, and in doing so, by-passed the local aircraft company, Commonwealth Aircraft Corporation.
CAC, under Sir Lawrence Wackett, began work on its own design, hoping to out-perform the Beaufort by building a machine that could serve as both a torpedo bomber and dive bomber. To keep down weight, Wackett dispensed with traditional self-sealing fuel tanks and opted to make the wing cavities liquid-tight, and thus serve as fuel storage. The Australian Government was initially uninterested in the CAC design. However, in mid-1940, cut off from the supply of British-made components for the Beaufort program (thanks to a British embargo on the export of aviation products, due to the need to maximise British production during the Battle of Britain), the Australian Government ordered a prototype of the CAC design, even before the Royal Australian Air Force had expressed a view about the machine. This prototype CA-4 took to the air on 19 September 1941. The CA-4 was a low wing, twin-engined, multi-role bomber with a crew of three. It was armed with four nose-mounted .303 calibre machine guns and two remote-controlled twin machine-gun barbettes mounted at the rear of the engine nacelles. It could carry either 500 lb (230 kg) bombs, 250 lb (110 kg) bombs or two torpedoes. It was originally powered by two Pratt & Whitney Twin Wasp R-1830-S3C3-G radials. Unfortunately, the novel fuel tanks never proved reliable, and in January 1943 the CA-4 prototype was completely destroyed in a mid-air explosion, probably due to a fuel leak.
With a re-designed tail and rudder, and an improved nose armament of two 20 mm cannon and two .303 calibre machine guns, the CA-4 became the CA-11 Woomera.