HMAS Pioneer was a Pelorus-class protected cruiser built for the Royal Navy at the end of the 19th century. She was transferred to the fledgling Royal Australian Navy (RAN) in 1912. During World War I, the cruiser captured two German merchant ships, and was involved in the East African Campaign, including the blockade of the cruiser SMS Königsberg and a bombardment of Dar-es-Salaam. She returned to Australia in late 1916 and was decommissioned. Pioneer was used as an accommodation ship for the following six years, then was stripped down and sold off by 1926. The cruiser was scuttled outside Sydney Heads in 1931.

The Pelorus-class cruiser was a "third-class" protected cruiser designed by Sir William White for the Royal Navy, based on the earlier Pearl-class cruisers. Eleven ships were ordered to this design in 1893 under the Spencer Programme, and were laid down 1896–1900. The first, HMS Pelorus, was commissioned in 1896.