HMHS Llandovery Castle, built in 1914 in Glasgow as RMS Llandovery Castle for the Union-Castle Line, was one of five Canadian hospital ships that served in the First World War. On a voyage from Halifax, Nova Scotia to Liverpool, England, the ship was torpedoed off southern Ireland on 27 June 1918. The sinking was the deadliest Canadian naval disaster of the war. 234 doctors, nurses, members of the Canadian Army Medical Corps, soldiers and seamen died in the sinking and subsequent machine-gunning of lifeboats. Twenty five people are known to have survived. 24 were the occupants on a single life-raft. The incident became infamous internationally and was considered, after the Armenian genocide, as one of the war's worst atrocities. After the war, the case of Llandovery Castle was one of six alleged German war crimes prosecuted at the Leipzig trials.

The Union-Castle Line was a British shipping line that operated a fleet of passenger liners and cargo ships between Europe and Africa from 1900 to 1977. It was formed from the merger of the Union Line and Castle Shipping Line.