In 1938, the Australian Commonwealth Naval Board (ACNB) identified the need for a general purpose 'local defence vessel' capable of both anti-submarine and mine-warfare duties, while easy to construct and operate.

[6] The need for locally built 'all-rounder' vessels at the start of World War II saw the "Australian Minesweepers" (designated as such to hide their anti-submarine capability, but popularly referred to as "corvettes") approved in September 1939, with 60 constructed during the course of the war: 36 (including Warrnambool) ordered by the RAN, 20 ordered by the British Admiralty but manned and commissioned as RAN vessels, and 4 for the Royal Indian Navy.

[1] A day later she was involved in the rescue of 73 crew from the Filipino merchant vessel MV Don Isidro, following attacks by Japanese dive bombers.

Over the next 12 months Warrnambool was involved in five evacuations or rescues (including that of HMAS Voyager’s crew following the destroyer running aground in September 1942), present for eighteen Japanese air raids, and transported over 4,000 troops to New Guinea.

[1] Following the conclusion of World War II, Warrnambool performed mine clearance work in the Solomon and New Guinea Islands before moving to the Great Barrier Reef.