804 Naval Air Squadron (804 NAS), also referred to as 804 Squadron, is an inactive Fleet Air Arm (FAA) naval air squadron of the United Kingdom's Royal Navy (RN). It most recently operated the Supermarine Scimitar F.1 jet fighter aircraft between March 1960 and September 1961, embarked in HMS Hermes and with a shore base at RNAS Lossiemouth, Moray.

It formed in November 1939 from part of 769 Naval Air Squadrons Gloster Sea Gladiators which had been detached to RNAS Hatston. It served throughout the Second World War with a further variety of fighter aircraft including Brewster Buffalo, Grumman Martlet, Hawker Sea Hurricane, Fairey Fulmar and Grumman Hellcat. The squadron was merged into 800 Naval Air Squadron in June 1944 and subsequently reformed in September, when it flew Supermarine Seafire. During the Korean War, it flew Hawker Sea Fury and these were followed by the Hawker Sea Hawk during the Suez Crises.

During World War II, the squadron was equipped with various aircraft types in differing roles. When formed, on 30 November 1939, at HMS Sparrowhawk, the Royal Naval Air Station near Kirkwall, on Mainland, Orkney, 804 used four Gloster Sea Gladiators in defence of the naval base at Scapa Flow, the aircraft were previously part of 769 Naval Air Squadron.

It transferred, in April 1940, to HMS Glorious to provide air cover for the ferrying of the Royal Air Force's 263 Squadron's Gloster Gladiators to Norway, after the German invasion. This was a brief assignment and in early May the squadron was transferred to HMS Furious via the Royal Naval Air Station at Campbeltown, thus missing HMS Glorious's sinking. Between May and September 1940, 804 Squadron returned to RNAS Hatston, and was subsequently recognised as one of the two FAA squadrons that operated with RAF Fighter Command in the Battle of Britain.

In October 1940, 804 Squadron re-equipped with Grumman Martlet Mk I, an American carrier-borne fighter aircraft, and first operated the new fighters out of RNAS Skaebrae in the Orkney Islands in October 1940. On 25 December 1940, two of the squadron's Grumman Martlets shot down a Junkers Ju 88 off Scapa Flow, thus scoring the first aerial victory in Europe by any variant of the Grumman F4F Wildcat. Further re-equipping occurred in February 1941 at RNAS Yeovilton (HMS Heron), Somerset, with Fairey Fulmar Mk II, a British carrier-borne fighter and reconnaissance aircraft and Hawker Sea Hurricane, a navalised version of the Hawker Hurricane fighter aircraft.

In April 1941 the squadron was assigned to operate from catapult-armed ships (CAM ships and fighter catapult ships) until this role was taken over by the RAF's Merchant Ship Fighter Unit in May 1942. During this assignment, the squadron had aircraft on HMS Ariguani, HMS Springbank (until sunk on 27 September 1940), HMS Maplin, and SS Michael (until sunk on 2 June 1941). In August 1941, an 804 Squadron Hawker Sea Hurricane from HMS Maplin, piloted by Robert Everett, shot down an Focke-Wulf Fw 200 Condor, the first such victory for a catapult launched aircraft.

In July 1942, the squadron escorted Gibraltar convoys on board the light aircraft carrier HMS Argus and later, in October, now equipped with Hawker Sea Hurricane Mk.IIc, joined the Avenger-class escort carrier HMS Dasher for the Operation Torch, the North African landings. The squadron was re-equipped yet again in August 1943 with Grumman Hellcat F. Mk. I, an American fighter aircraft and in October formed part of the 7th Naval Fighter Wing. Two months later they embarked on the Ruler-class escort carrier HMS Emperor and accompanied a US-bound convoy.

The squadron took part in the successful assault on 3 April 1944, against the German battleship Tirpitz as part of Operation Tungsten in Altafjord, located in northern Norway. The Fleet Air Arm's Fairey Barracuda dive-bombers launched from HMS Furious and HMS Victorious received support from the 7th Naval Fighter Wing, which included 804. However, in June 1944, 804 was absorbed into 800 Squadron.