The Commander-in-Chief Fleet (CINCFLEET) was the admiral responsible for the operations of the ships, submarines and aircraft of the British Royal Navy from 1971 until April 2012.

The post was subordinate to the First Sea Lord, the professional head of the Naval Service.

Previous to November 1971, on 1 May 1971 CINCWF had already assumed responsibility for the administration of ships in the Far East Fleet.

In 2005, the Second Sea Lord, reduced in rank from full Admiral to Vice-Admiral, came under CINCFLEET's command, a situation that lasted until the Levene reforms of 2012.

[9] In 1971 after the amalgamation of the Western and Far East Fleets the headquarters was established at Northwood, in the London Borough of Hillingdon (HMS Warrior).

[9][dead link‍] By the 2010s, CINCFLEET was supported by:[9][dead link‍] Collectively, COMUKMARFOR, COMUKAMPHIBFOR, Commander UK Task Group (COMUKTG), and the 3 Commando Brigade Headquarters comprised the "Fleet Battle Staff".

The Flag Officer, Third Flotilla was a rear admiral based at HMNB Portsmouth who doubled as NATO Commander Anti-Submarine Warfare Striking Force.

Additionally the Second Flotilla's 3rd Destroyer Squadron was based at RN Dockyard Rosyth.

In war FOSNI would have been one of two naval operational commands, with the other being Flag Officer Plymouth.