In September 1915, Rostron joined the RMS Mauretania and in April 1916 he joined the Ivernia in the Mediterranean Sea. He returned to Mauretania in 1917 before taking command of the Andania, Saxonia, Carmania and Mauretania again. An acting captain in the RNR at war's end, he was promoted to captain in the RNR on 31 December 1918 and made a Commander of the Order of the British Empire in the 1919 New Year Honours list.
