Hospital ship in the context of "USNS Mercy (T-AH-19)"

An ocean liner is a type of passenger ship primarily used for transportation across seas or oceans. Ocean liners may also carry cargo or mail, and may sometimes be used for other purposes (such as for pleasure cruises or as hospital ships). The Queen Mary 2 is the only active ocean liner in 2025, serving with Cunard Line.

The category does not include ferries or other vessels engaged in short-sea trading, nor dedicated cruise ships where the voyage itself, and not transportation, is the primary purpose of the trip. Nor does it include tramp steamers, even those equipped to handle limited numbers of passengers. Some shipping companies refer to themselves as "lines" and their passenger ships, which often operate over set routes according to established schedules, as "liners".

Kasato Maru or Kasado Maru (Japanese: 笠戸丸) was a Japanese cargo/passenger ship built by the British shipyard Wigham Richardson in 1900. Originally christened as SS Potosí, the ship was bought by the Russian Dobroflot, and renamed Kazan, being used as a hospital ship. She was sunk by the Japanese Navy during the Russo-Japanese War, salvaged and passed to the Japanese control as compensation for war.

She was adapted to be a passenger ship and renamed as Kasato Maru and transported the soldiers who had fought in Manchuria back to Japan.

HMS Discovery was a Royal Navy ship launched in 1789 and best known as the lead ship in George Vancouver's exploration of the west coast of North America in his famous 1791-1795 expedition. She was converted to a bomb vessel in 1798 and participated in the Battle of Copenhagen. Thereafter she served as a hospital ship and later as a prison hulk until 1831. She was broken up in 1834.