Originally built for the Navigazione Generale Italiana (NGI) as SS Guglielmo Marconi, its state-ordered merger with the Lloyd Sabaudo line meant that the ship sailed for the newly created Italia Flotta Riunite (Italian Line).Rex operated transatlantic crossings to America from Italy with its running mate, Conte di Savoia prior to the outbreak of the Second World War. Rex maintained a commercial service in the Mediterranean Sea for a short period, but when Italy entered the war in June 1940 Rex was laid up for safe-keeping. On 8 September 1944, off Koper, Rex was hit by 123 rockets launched by Royal Air Force aircraft, caught fire from stem to stern.