In February 1938 the Australian Commonwealth Naval Board (ACNB), which consisted of both government officials and flag officers of the Australian navy, defined that there was an urgent requirement for several dozens of military vessels for local defense and guard duties. The ships would have to be built both cheap and simple so there was a need for a simple and basic design. The basic requirements were defined by a displacement of approximately 500 tons, a speed of approximately 10 knots and a range of 2,000 nautical miles. The vessels would be used for mine detection and for submarine hunting. Soon it became clear that the basic requirements, as proposed by the ACNB, would not completely comply.