HMS Hood (pennant number 51) was a battlecruiser of the Royal Navy. Hood was the first of the planned four Admiral-class battlecruisers to be built during World War I. Already under construction when the Battle of Jutland occurred in mid-1916, that battle revealed serious flaws in her design despite drastic revisions before she was completed four years later. For this reason, she was the only ship of her class to be completed, as the Admiralty decided it would be better to start with a clean design on succeeding battlecruisers, leading to the never-built G-3 Class.