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 . She was accompanied by , and . H3 was mined in the Gulf of Cattaro, Adriatic on 15 July 1916.
She had a displacement of at the surface and while submerged. Her total length was , with a beam of and a draught of .
Her two diesel engines provided a total power of and her two electric motors provided power which gave the submarine a maximum surface speed of and a submerged speed of . She would normally carry of fuel and had a maximum capacity of and a range of . The boat was armed with a Hotchkiss quick-firing gun and four bow torpedo tubes with six torpedoes carried. The complement was twenty-two crew members.