Her or His Majesty's Australian Ship (HMAS) is a ship prefix used for commissioned units of the Royal Australian Navy. This prefix is derived from HMS , the prefix used by the Royal Navy of the United Kingdom, and can be equally applied to warships and shore bases (as Australia follows the British tradition of referring to naval establishments as ships or stone frigates). The prefix came into use in October 1911, when King George V of the United Kingdom fixed his signature to the approval for the Royal Australian Navy.
The prefix refers to the King or Queen of Australia, who is also equally and separately the British monarch. The first word of the prefix changes depending on the gender of the reigning Australian monarch.