Originally formed from 450 Flight in Apr 1933 as a Fleet Spotter unit but it became an Anti-Submarine unit during WWII when it served with distinction, disbanding in Mar 1946. Further commissions came and went and it disbanded once again in Dec 1957, bringing its history as a fixed-wing unit to a close.
820 Squadron was the second anti-submarine helicopter unit to form in Jan 1958 with the Whirlwind HAS.7 at RNAS Eglinton. The first HAS.7s experienced a series of engine problems and whilst in the Far East, engines were swapped over. The unit disbanded at Sembawang on 8 May 1959, when the HAS.7 was grounded. Once HAS.7 operations were resumed, it reformed in the UK at RNAS Culdrose in Nov 1959, still with Whirwind HAS.7s, where it disbanded again in Oct 1960. It re-emerged with Wessex HAS.1 at Culdrose in Sep 1964 and deployed in Dec 1964 to the Far East via the Indian Ocean on HMS Eagle
(R05), finally returning in Jun 1968.
During May 1969, the Wessex HAS.1 was phased out for 4 of the more capable Wessex HAS.3, which deployed with HMS Blake
(C99) and the occasional Fleet Tanker auxiliary over the next few years. In Dec 1972, the Sea King HAS.1 replaced the Wessex in the anti-submarine role and spent Sep 1974 to Jun 1975 embarked on HMS Blake. These in turn were updated by the Sea King HAS.2 in Jan 1977 and the short-lived HAS.2A in Jan 1979, prior to transferring to HMS Hermes
(R12) in Jan 1980.
It disembarked from HMS Hermes (R12) to RNAS Culdrose
in Mar 1980 and replaced the HAS.2As with the Sea King
HAS.5 in Nov 1980 in time to work up with HMS Invincible (R05), embarking in Feb 1981. The Squadron was involved in intensive flying in the South Atlantic
, operating briefly from San Carlos during Jun 1982. After a brief Far East tour, the unit returned to the UK in Mar 1984 when HMS Invincible developed mechanical difficulties.
Further deployments followed, including the transfer to HMS Ark Royal (R07) during early 1986 for later deployments to the Far East and Australia
. On 10 Jan 1991, it embarked HMS Ark Royal
with 10 Sea Kings to patrol the Mediterranean gateway to the Suez Canal during the Gulf War. The unit was a key player during 1993 in the NATO intervention in Bosnia and then transferred to HMS Illustrious (R06) in Autumn 1994, followed by service in the Gulf during late 1998. The Merlin
HM.1 was cautiously introduced as a single Flight from Sep 2001 and dual operation with the Sea King HAS.6 continued until Mar 2003 when the Sea King was finally retired after recovering embarked flights (such as RFA Fort Austin
), leaving 820 Squadron to become a Merlin only unit, officially from Sep 2003.