Hood was a battlecruiser - one of a new breed of warships developed before the First World War. With more horsepower and less armour, they were faster than battleships and were designed to outrun and outgun enemy ships.
Their vulnerability became clear in the Battle of Jutland in 1916, when three battlecruisers were lost. All three were struck by gunfire which penetrated their thin deck- and turret-armour.
Despite this tragic loss, the Admiralty went on to build Hood. She was improved in a number of ways but still lacked armour protection.
British battlecruiser HOOD.
September, 1933. Crown Copyright
Launched on 22 August 1918, HMS Hood was the 13th and final British battlecruiser. Big, fast and powerful, for the population at home, she was a symbol of Britain's supremacy in the world. However, she was an old ship, due for modernisation. The Navy knew that, like her predecessors, she would be vulnerable to plunging shell fire. But she was too urgently needed to be spared for a full refit.
Bismarck, in contrast, was a much more modern ship. The 1919 Versailles Treaty severely restricted Germany's ability to re-arm after the First World War. These restrictions were not lifted until Britain and Germany signed the Anglo-German Naval Agreement in 1935.
That allowed Germany to build a surface fleet of up to 35% of the size of Britain's, and up to 45% in the case of submarines. Five months later, Bismarck's design was complete.
Bismarck, May 1941, taken from Prinz Eugen
She was launched on 14 February 1939. One of the most significant characteristics of this new ship was her ability to withstand damage. The design of her armour meant she was very well defended against any potential adversary. Armed, too, with powerful 38cm guns, she looked invincible.