HMS H3

HMS H3 was a British H-class submarine built by Canadian Vickers Co, Montreal. She was laid down on 11 January 1915 and was commissioned on 3 June 1915.

After commissioning she crossed the Atlantic from St. John's, Newfoundland to Gibraltar escorted by the armed merchant cruiser HMS Calgarian (1913). She was accompanied by HMS H1, HMS H2 and HMS H4.

H3 was mined in the Gulf of Cattaro, Adriatic on 15 July 1916.