Following the opening of the Sydney Harbour Bridge, both ferries were redundant. During World War II, they were requisitioned by the Royal Australian Navy. "Kuttabul" was sunk during the 1942 Japanese Attack on Sydney Harbour with the loss of 19 lives. "Koompartoo" was converted to a boom defence vessel and taken to Darwin. Following the War, she was laid up in Sydney until 1962 when she was taken to Launceston, Tasmania where her hull was used as bauxite barge. Her final fate is unclear.