World War I: The Royal Navy defeats the German fleet in the Battle of Heligoland Bight.

The Battle of Heligoland Bight was the first Anglo-German naval battle of the First World War, fought on 28 August 1914, between ships of the United Kingdom and Germany. The battle took place in the south-eastern North Sea, when the British attacked German patrols off the north-west German coast. The German High Seas Fleet was in harbour on the north German coast while the British Grand Fleet was out in the northern North Sea. Both sides engaged in long-distance sorties with cruisers and battlecruisers, with close reconnaissance of the area of sea near the German coastthe Heligoland Bightby destroyer.

The British devised a plan to ambush German destroyers on their daily patrols. A British flotilla of 31 destroyers and two cruisers under Commodore Reginald Tyrwhitt, with submarines commanded by Commodore Roger Keyes, was dispatched. They were supported at longer range by an additional six light cruisers commanded by William Goodenough and five battlecruisers commanded by Vice Admiral David Beatty.

Surprised, outnumbered and outgunned, the German fleet suffered 712 sailors killed, 530 injured and 336 taken prisoner; three German light cruisers and one torpedo boat were sunk; three light cruisers and three torpedo boats suffered damage. The British suffered casualties of 35 killed and 55 wounded; one light cruiser and three destroyers suffered damage. Despite the disparity of the ships involved in the battle, the battle was regarded as a great victory in Britain, where the returning ships were met by cheering crowds.

Beatty was vaunted as a hero, although he had taken little part in the action or planning of the raid, which was led by Commodore Tyrwhitt and conceived by him and Keyes, who had persuaded the Admiralty to adopt it. The raid might have led to disaster, had the additional forces under Beatty not been sent by Admiral John Jellicoe at the last minute. The German government and the Kaiser in particular, restricted the freedom of action of the German fleet, instructing it to avoid any contact with superior forces for several months thereafter.

World War I, often abbreviated as WWI or WW1, also known as the First World War and contemporaneously known as the Great War and by other names, was an international conflict that began on 28 July 1914 and ended on 11 November 1918. It involved much of Europe, as well as Russia, the United States and Turkey, and was also fought in the Middle East, Africa and parts of Asia. One of the deadliest conflicts in history, an estimated 9 million were killed in combat, while over 5 million civilians died from occupation, bombardment, hunger or disease. The genocides perpetrated by the Ottomans and the 1918 Spanish flu pandemic spread by the movement of combatants during the war caused many millions of additional deaths worldwide.In 1914, the Great Powers were divided into two opposing alliances: the Triple Entente, consisting of France, Russia, and Britain, and the Triple Alliance, made up of Germany, Austria-Hungary, and Italy. Tensions in the Balkans came to a head on 28 June 1914 following the assassination of Archduke Franz Ferdinand, the Austro-Hungarian heir, by Gavrilo Princip, a Bosnian Serb. Austria-Hungary blamed Serbia and the interlocking alliances involved the Powers in a series of diplomatic exchanges known as the July Crisis. On 28 July, Austria-Hungary declared war on Serbia; Russia came to Serbia's defence and by 4 August, the conflict had expanded to include Germany, France and Britain, along with their respective colonial empires. In November, the Ottoman Empire, Germany and Austria formed the Central Powers, while in April 1915, Italy joined Britain, France, Russia and Serbia as the Allied Powers.

Facing a war on two fronts, German strategy in 1914 was to defeat France, then shift its forces to the East and knock out Russia, commonly known as the Schlieffen Plan. This failed when their advance into France was halted at the Marne; by the end of 1914, the two sides faced each other along the Western Front, a continuous series of trench lines stretching from the Channel to Switzerland that changed little until 1917. By contrast, the Eastern Front was far more fluid, with Austria-Hungary and Russia gaining, then losing large swathes of territory. Other significant theatres included the Middle East, the Alpine Front and the Balkans, bringing Bulgaria, Romania and Greece into the war.

Shortages caused by the Allied naval blockade led Germany to initiate unrestricted submarine warfare in early 1917, bringing the previously neutral United States into the war on 6 April 1917. In Russia, the Bolsheviks seized power in the 1917 October Revolution and made peace in the March 1918 Treaty of Brest-Litovsk, freeing up large numbers of German troops. By transferring these to the Western Front, the German General Staff hoped to win a decisive victory before American reinforcements could impact the war, and launched the March 1918 German spring offensive. Despite initial success, it was soon halted by heavy casualties and ferocious defence; in August, the Allies launched the Hundred Days Offensive and although the German army continued to fight hard, it could no longer halt their advance.Towards the end of 1918, the Central Powers began to collapse; Bulgaria signed an Armistice on 29 September, followed by the Ottomans on 31 October, then Austria-Hungary on 3 November. Isolated, facing revolution at home and an army on the verge of mutiny, Kaiser Wilhelm abdicated on 9 November and the new German government signed the Armistice of 11 November 1918, bringing the fighting to a close. The 1919 Paris Peace Conference imposed various settlements on the defeated powers, the best known being the Treaty of Versailles. The dissolution of the Russian, German, Ottoman and Austro-Hungarian empires led to numerous uprisings and the creation of independent states, including Poland, Czechoslovakia and Yugoslavia. For reasons that are still debated, failure to manage the instability that resulted from this upheaval during the interwar period ended with the outbreak of World War II in 1939.