Royal Mail Ship

Royal Mail Ship (or Steamer), usually seen in its abbreviated form RMS, is the ship prefix used of any seagoing vessel that carries mail under contract to the British Royal Mail. The designation has been used since the 1840s; the Cunard line came to hold most of the mail contract business, and all of its ships were traditionally entitled "RMS". Technically, a ship would use the prefix only while contracted to carry mail, and would revert to a standard type designation such as "SS".

In recent years the shift to air transport for mail has left only a few ships with the right to the prefix; notably RMS St. Helena, which serves the island of St. Helena in the South Atlantic, and RMS Queen Mary 2.

RMMV, for Royal Mail Motor Vessel, and RMMS, for Royal Mail Motor Ship, are also sometimes seen, but much less commonly.