Royal Mail Ship

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".

The most valuable route, with the highest volume, was between Kingstown (now Dún Laoghaire), in Ireland, and Holyhead in Wales.

In recent years the shift to air transport for mail has left only three ships with the right to the prefix or its variations: RMS Segwun, which serves as a passenger vessel in Gravenhurst, Ontario, Canada; RMV Scillonian III, which serves the Isles of Scilly; and RMS Queen Mary 2.

The "RMS" prefix was granted to QM2 by Royal Mail when she entered service in 2004 on the Southampton to New York route as a gesture to Cunard's history.

The UK's flag carrier airline, British Airways, is contracted to carry mail on some of its scheduled long-distance routes.