The Commonwealth Aircraft Corporation of Australia had acquired a license to build the Pratt & Whitney Wasp S1H-1G single-row air-cooled radial engine. Since many components of this engine were compatible with the fourteen-cylinder Twin Wasp, the RAAF elected to have Pratt & Whitney Twin Wasp SC3-Gs (rated at 1050 hp for takeoff and 900 hp at 12,000 feet) fitted to the fifty Hudsons that it ordered. These aircraft were built as Model B14S, RAAF serials A16-1 to A16-50 were assigned (construction numbers B14L-1750, 1778/1779, 1855/1900, 1903. Initial delivery took place on February 9, 1940. These were initially known as Mk.Is, but they were later redesignated Hudson Mk.IV to avoid confusion with the Cyclone-powered Mk.Is of the RAF. The first batch of aircraft was delivered without dorsal turrets and had a flexible gun in a dorsal hatch.
A follow-on order was issued for 50 more aircraft (RAAF serials A16-51 through A16-100, c/ns B-14L-1904/1920, 1931/1954). These aircraft incorporated a number of minor improvements. They were initially known as Hudson Mk.IIs, but to avoid confusion with the RAF Mk.IIs, they were redesignated Hudson Mk.IV.
30 aircraft (AE609/AE638, construction numbers 414-2383/2500, 2590/2601) generally similar to the RAAF Hudson Mk.IIs were ordered for the RAF, with 23 being delivered to Britain and seven going to Australia. They were also known as Mk.IV, just like the aircraft for Australia.