HMS H5 was a British H-class submarine of the Royal Navy that served in the First World War.

The boat, which was launched on 1 April 1915, was lost after being rammed by a British merchant ship off Caernarfon Bay in March 1918.

[2] H5 was fitted with a 6 pounds (2.7 kg) Hotchkiss quick-firing gun (6-pounder) and four 18 inches (460 mm) torpedo tubes.

[5] HMS H5 was sunk after being rammed by the British merchantman Rutherglen when mistaken for a German U-boat on 2 March 1918.

All on board perished including a US Navy observer, Lieutenant Earle Wayne Freed Childs from the American submarine AL-2.