RMS Dunottar Castle was a Royal Mail Ship that went into service with the Castle Line (and its successor, the Union-Castle Line) in 1890 on the passenger and mail service between Britain and South Africa. In 1913 the ship was sold to the Royal Mail Steam Packet Company as the Caribbean. After the outbreak of the First World War she served as HMS Caribbean, first as a troop ship and then as an Armed Merchant Cruiser, until she sank in a storm off the Scottish coast on 27 September 1915.