for the type were obtained from North American Aviation along with an accompanying arrangement to domestically produce the Wirraway's Wasp engine from Pratt & Whitney. Additionally, a pair of NA-16s were purchased directly from North American to act as prototypes. The first of these two aircraft was the fixed undercarriage NA-16-1A (similar in design to the BT-9); the second was the retractable undercarriage NA-16-2K (similar to the BC-1). These two aircraft were also known by their NAA project accounting codes (NA-32 for the NA-16-1A and NA-33 for the NA-16-2K) sometimes leading to confusion; these accounting codes (or "charge" codes) were used internally by NAA to track their projects and were not the actual aircraft model numbers. During August 1937, the NA-16-1A arrived in Australia and, following its re-assembly, flew for the first time at Laverton on 3 September of that year, exactly two years before war was declared on Nazi Germany by the United Kingdom and France. During September 1937, the NA-16-2K arrived in Australia and likewise flew shortly afterwards. These aircraft were given the RAAF serials A20-1 and A20-2 within that organisation's numbering system. Production The NA-16-2K model was the type selected for initial production. The design featured several detail and structural changes, such as provisions for the fitting of a pair of forward-firing guns instead of the NA-16's single gun, and the strengthening of the tail and wings to better facilitate dive-bombing operations. Other modifications included the adoption of a single gun set on a swivelling mount to the rear of the cockpit, along with the installation of cameras and radio sets. On 27 March 1939, the first CA-1 Wirraway, RAAF serial A20-3, performed its maiden flight. This aircraft was subsequently retained by CAC for evaluation and trials for a number of months; on 10 July 1939, the first pair of Wirraways to be delivered to the RAAF, serials A20-4 and A20-5, were received by the service. By the outbreak of the Second World War, the RAAF had received a total of six Wirraways. Early on, it became clear that CAC's rate of manufacture of the airframes outstripped Australian capacity to produce the Wasp engines to power the type. During 1940, having observed an excess of Australian capacity, Britain issued an offer to procure any Wirraway airframes that could be produced that had not already been allocated to fulfil RAAF orders, intending to fit US-built Wasp engines to