HMS H3 was a British H-class submarine built by Canadian Vickers Co, Montreal.

After commissioning she crossed the Atlantic from St. John's, Newfoundland to Gibraltar escorted by the armed merchant cruiser HMS Calgarian.

British H-class submarines had ranges of 1,600 nautical miles (3,000 km; 1,800 mi).

[2] H3 was fitted with a 6 pounds (2.7 kg) Hotchkiss quick-firing gun (6-pounder) and four 18 inches (460 mm) torpedo tubes.

[2] It is a Holland 602 type submarine but was designed to meet Royal Navy specifications.