What does U.S.S. mean in ship names?

U.S.S. (USS) preceding the names of vessels are the abbreviation of United States Ship. It is frequently but erroneously stated that the second S stands for Steamship or Steamer. But these letters were use$ in this connection before the days of steam-propelled vessels. They are used only with the names of vessels in the United States Navy; as, U.S.S. “Texas,” U.S.S. “Maine.” The names of vessels in the United States, merchant marine are preceded by the letters S.S.; as, S.SL “Leviathan.” S.S”. is the official abbreviation for steamship. HM.S. preceding the name. of a. vessel stands for His (or Her) Majesty’s Ship. The letters are used in connection only with vessels in the British service. Popularly HM.’.S. is supposed to be the abbreviation of His Majesty’s Steamer, but the letters were used in the names of British ships long before the commercial development of the steamboat. HM.S. is also the abbreviation of His Majesty’s Service.