Royal Mail Ship

Royal Mail Ship (sometimes Steam-ship or Steamer), usually seen in its abbreviated form RMS, is the ship prefix used for seagoing vessels that carry mail under contract to the British Royal Mail. The designation dates back to 1840.^[1] Any vessel designated as "RMS" has the right both to fly the pennant of the Royal Mail when sailing and to include the Royal Mail "crown" insignia with any identifying device and/or design for the ship.^[2][3][4]

It was used by many shipping lines, but is often associated in particular with the White Star Line, Cunard Line,^[2][5] Royal Mail Lines, Union-Castle Line, Canadian Pacific Line, Orient Line and the P&OSNC, which held a number of high-profile mail contracts, and traditionally prefixed the names of many of their ships with the initials "RMS".

While some lines in the past, particularly the Royal Mail Lines, called all their ships "RMS", technically a ship would use the prefix only while contracted to carry mail, and would revert at other times to a standard designation such as "SS".^[6][7]