HMS H1 was a H-class submarine built by Canadian Vickers Co., Montreal for the British Royal Navy. She was laid down on 11 January 1915 and was commissioned on 26 May 1915. H1 crossed the Atlantic from St. John's, Newfoundland to Gibraltar escorted by the armed merchant cruiser HMS Calgarian. She was accompanied by H2, H3 and H4. H1 mistakenly sank the Italian submarine off Cattaro on 15 April 1918. H1 was sold on 7 March 1921 in Malta.