The Wirraway (meaning 'Challenge' in Aboriginal) was a modified version of the North American NA-33. The original single wing-gun was replaced by twin synchronised guns in blast troughs above the fuselage, plus a flexible gun in the rear cockpit. Camera and radio installations were introduced, and the wing and tail units were redesigned and strengthened for dive-bombing in later variants only. The first Wirraway, A20-3, was test flown by Flight Lieutenant 'Boss' Walker on 27 March 1939, and the first three RAAF Wirraways were accepted in July 1939. By December 1940, seven aircraft were being delivered weekly, and by September 1941, 45 Wirraways per month were coming off the production line. The initial orders for 620 aircraft were completed by June 1942, but limited production continued until 1946 when the 755th Wirraway, A20-757, was delivered. CAC designations for Wirraway orders included CA-1, -3, -5, -7, -8, -9, -10 (a bomber version which was cancelled), -10A (dive bomber), and -16. The designation CA-20 covered the conversion of Wirraways for the RAN. In 1940-41, camouflaged Wirraways were deployed to forward bases in Malaya (No 21 Squadron) Rabaul (No 24 Squadron), and Darwin (No 12 Squadron). On 6 January 1942, Flight Lieutenant B. Anderson of No 24 Squadron became the first RAAF pilot to engage in air-to-air combat in the South-West Pacific, when his Wirraway intercepted a Kawanishi (Mavis) flying-boat over Rabaul. Two weeks later, on 20 January 1942, the Rabaul Wirraways achieved immortal fame when eight aircraft, including A20-177, piloted by Sergeant W. Hewett, courageously engaged a force of over 100 Japanese fighters and bombers. Although hopelessly outclassed by enemy aircraft, the Wirraway remained in the front line as a stop-gap fighter, and on 26 December 1942, Wirraway history was made when Pilot Officer J. Archer, in A20-103, succeeded in shooting down a Zero fighter near Gona.