HMS Porpoise was the former mercantile quarter-decked sloop Lord Melville, which the Royal Navy purchased in 1804 to use as a store-ship. She sailed to the colony of New South Wales in January 1806, arriving seven months later. She was the flagship of William Bligh when he was governor of New South Wales and played a prominent role in the Rum Rebellion. In May 1810 Porpoise sailed from Sydney; after arriving in Britain she underwent a major refit. After voyages to the West Indies, the Cape of Good Hope and North America she served as a harbour ship at Woolwich and Sheerness. She was laid up in 1814 and sold in January 1816.