Her Majesty's Australian Ship

Her or His Majesty's Australian Ship (HMAS) is a ship prefix used for commissioned units of the Royal Australian Navy (RAN). This prefix is derived from HMS (Her/His Majesty's Ship), 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).

On 10 July 1911, King George V granted the title of Royal Australian Navy to the naval forces of Australia. At the same time, the prefix and acronym were approved for use in identifying units commissioned into the RAN. The prefix had been used prior to formal approval, with the torpedo-boat destroyer HMAS Parramatta (D55) commissioned with the HMAS prefix on 1 March 1911.

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.