John Fisher, 1st Baron Fisher in the context of "Reserve Fleet (United Kingdom)"

HMS Repulse was one of two Renown-class battlecruisers built for the Royal Navy during the First World War. Originally laid down as an improved version of the Revenge-class battleship, her construction was suspended on the outbreak of war because she would not be ready in time. Admiral Lord Fisher, upon becoming First Sea Lord, gained approval for her to resume construction as a battlecruiser that could be built and enter service quickly. The Director of Naval Construction (DNC), Eustace Tennyson-d'Eyncourt, quickly produced an entirely new design to meet Admiral Lord Fisher's requirements and the builders agreed to deliver the ship in 15 months. They did not quite meet that ambitious goal, but the ship was delivered a few months after the Battle of Jutland in 1916. Repulse and her sister ship Renown were the world's fastest capital ships upon completion.

Repulse participated in the Second Battle of Heligoland Bight in 1917, the only combat she saw during the war. She was reconstructed twice between the wars; a reconstruction in the 1920s increased her armour protection and made lesser improvements, while another in the 1930s was much more thorough. Repulse accompanied the battlecruiser Hood during the Cruise of the Special Service Squadron on a round-the-world cruise in 1923 to 1924 and protected international shipping during the Spanish Civil War in 1936 to 1939.

HMS Renown was the lead ship of her class of battlecruisers of the Royal Navy built during the First World War. She was originally laid down as an improved version of the Revenge-class battleships. Her construction was suspended on the outbreak of war on the grounds she would not be ready in time. Admiral Lord Fisher, upon becoming First Sea Lord, gained approval to restart her construction as a battlecruiser that could be built and enter service quickly. The Director of Naval Construction (DNC), Eustace Tennyson-d'Eyncourt, quickly produced a new design to meet Fisher's requirements and the builders agreed to deliver the ships in 15 months. They did not quite meet that ambitious goal but the ship was delivered a few months after the Battle of Jutland in 1916. Renown, and her sister HMS Repulse, were the world's fastest capital ships upon completion.

Renown did not see action during the war and was reconstructed twice between the wars; the 1920s reconstruction increased her armour protection and made other more minor improvements; the 1930s reconstruction was much more thorough. The ship frequently conveyed royalty on their foreign tours and served as flagship of the Battlecruiser Squadron when Hood was refitting.

First Sea Lord, officially First Sea Lord and Chief of the Naval Staff (1SL/CNS), is a statutory position in the British Armed Forces, held by an admiral or a general of His Majesty's Naval Service. As the highest-ranking officer in the Naval Service, the chief is the principal military advisor on matters pertaining to the navy and a deputy to the Secretary of State for Defence. The CNS is also a member of the Chiefs of Staff Committee and, thereby, a military advisor to the National Security Council, the prime minister and the monarch. The First Sea Lord is typically the highest-ranking officer on active duty of the Royal Navy unless the Chief of the Defence Staff is a naval officer. The post is currently held by General Sir Gwyn Jenkins.

Originally titled the "Senior Naval Lord to the Board of Admiralty" when the post was created in 1689, the office was re-styled First Naval Lord in 1771. The concept of a professional "First Naval Lord" was introduced in 1805, and the title of the office was changed to First Sea Lord on the appointment of Sir John "Jackie" Fisher in 1904. Since 1923, the First Sea Lord has been a member of the Chiefs of Staff Committee; they now sit on the Defence Council and the Admiralty Board.