The Great War
Britannia no longer rules the waves as the Royal Navy suffers shattering defeats, the worst being at Coronel, off the Chilean coast.
During the First World War most of the Royal Navy's strength was deployed at home in the Grand Fleet, confronting the German High Seas Fleet across the North Sea. A few inconclusive clashes took place between them, chiefly the Battle of Jutland in 1916. These exposed the deficiencies of a British approach to capital ship design which prioritised speed and firepower, as against the German emphasis on resilience, as well as the inadequacies of Britain's hastily-assembled munitions industry. However, the Germans were repeatedly outmaneuvered and the British numerical advantage proved insurmountable, leading the High Seas Fleet to abandon its challenge to British dominance.
Elsewhere in the world, the Navy hunted down the handful of German surface raiders at large. During the Dardanelles Campaign against the Ottoman Empire in 1915 it suffered serious losses during a failed attempt to break through the system of minefields and shore batteries defending the straits.
Upon entering the First World War, the British immediately established a blockade of Germany. The Navy's Northern Patrol closed off access to the North Sea, while the Dover Patrol closed off access to the English Channel. The Navy also mined the North Sea. As well as attempting to close off the Imperial German Navy's access to the Atlantic, the blockade was also designed to stop merchant shipping heading to or from Germany. The blockade was maintained eight months after the war had ended in order to force Germany to sign the Treaty of Versailles.
The most serious menace faced by the Navy came from the attacks on merchant shipping mounted by German U-boats. For much of the war this submarine campaign was restricted by prize rules requiring merchant ships to be warned and evacuated before sinking. In 1915 the Germans renounced these restrictions and began to sink merchant ships on sight, but later returned to the previous rules of engagement to placate neutral opinion. A resumption of unrestricted submarine warfare in 1917 raised the prospect of Britain and its allies being starved into submission. The Navy's response to this new form of warfare had proved inadequate due to its refusal to adopt a convoy system for merchant shipping, despite the demonstrated effectiveness of the technique in protecting troop ships. The belated introduction of convoys sharply reduced losses and brought the U-boat threat under control.