On entering the Great War, The Royal Navy was in good shape. It had just undergone beneficial reforms undertaken by Admiral Sir John Fisher, the First Sea Lord 1904-1910, who would return early in the war. It was also the pioneer of the Dreadnought-type battleship.

The Navy was constructed on the basis of the 'two-power standard', in that Britain's Navy should be the equal to that of any other two nations combined. When the war opened, this was very nearly the case.

Unfortunately, the Royal Navy never had a chance to prove its seapower conclusively, and the only major naval engagement at Jutland was inconclusive despite being a major strategic victory. The Navy was organized in squadrons of capital ships to form the battle-fleet, of which the battlecruisers formed the reconnaissance element yet capable of engaging the enemy's main body, with lighter cruisers used as a support for the main fleet and to patrol the sea lanes around the world.

The war saw the Navy move away from heavy cruisers and the increasing significance of light cruisers, the first three light cruiser squadrons being formed in early 1915, by the end of 1918 only one Cruiser Squadron remained with the Grand Fleet. All other cruisers squadrons being light cruisers of between four and six ship each, compared to the eleven cruiser squadrons active at the beginning of the war, of between four and eight ships apiece.

Destroyers evolved from the early 'torpedo-boat destroyers' to much larger, swifter and more powerfully-armed ocean going vessels. Destroyers were organized in flotillas of varying sizes, some numbering more than 20 ships. There were nine flotillas in 1914, rising to 16 in 1916 based in home waters, with a smaller number on foreign stations. Light cruisers or specially built ships were used as leaders for flotillas.

Submarines were a recent development, and was regarded as an un-English method of warfare. The size of the submarines increased during the war, ranging from 165 tons of the A Class to 1,880 ton K class in 1917-1918. The K class were fleet submarines designed to accompany the battlefleet. M Class submarines mounted a 12inch gun for shore bombardment and the R Class completed in 1918, were designed to hunt U-Boats. Seaplane carriers, Monitors, Merchant cruisers and Q-ships were also in the inventory.

After the First World War, the Royal Navy, saw to the destruction of the German High-Seas fleet at Scapa Flow and then saw a decline in ship numbers and personnel as did the other services prior to World War 2, but was still required to maintain the overseas colonies. The greatest lack that the Navy suffered entering World War 2, was not a lack of carriers or destroyers, but a lack of refuelling ships which would hurt them badly in operations against the Japanese and Bismarck during the War. This lack forced ships to return to base to refuel frequently. Once the German U-Boat threat became apparent huge numbers of escorts were needed as well as support from the RAF Coastal Command, which was short of desperately needed aircraft. The Fleet Air Arms fighters were obsolete, and so in theory-was the Fairey Swordfish, although the 'stringbag' would prove itself more than equal to its replacement at Taranto and in the destruction of the Bismarck.

The Royal Navy's history in World War 2, was the most active of the two wars, and was in action in all of the worlds Oceans. Although, as in World War One, there was no decisive battleship to battleship engagement, apart from the Bismarck chase which resulted in a two on one one-sided engagement after the Navy has suffered the devastating loss of the HMS Hood. The Second World War also saw the carrier replace the battleship as the premier weapon of the Navy, and the carrier achieved some notable victories in the war including the crippling of the Bismarck, the destruction of the Italian Fleet at Taranto (Which gave the Japanese the idea for Pearl Harbour), and the powerful capabilities of aircraft which could hunt U-boats at sea from the Convoy Escort carriers in the north Atlantic, and Arctic Oceans

Although the battleship also had some impressive accomplishments in the war, it was already doomed, these actions included the destruction of the Bismarck, the Mediterranean campaigns including the Battle of Matapan which saw the Italian fleet defeated and afraid to ever engage the Mediterranean Fleet again.

The Second World War saw some interesting and violent cruiser and destroyer actions such as the Battle of of the North Cape, the Battle of the River Plate and the Bismarck chase. The destroyers also played a vital role in the convoys and every amphibious operation in World War 2.