The squadron's first assignment on its formation was to carry out spotter-reconnaissance duties for the aircraft carrier . They were later re-equipped with Fairey Seals and Blackburn Sharks, eventually receiving Fairey Swordfish in autumn 1937. The squadron was reassigned in November the following year to the new aircraft carrier . The squadron operated from "Ark Royal" for the next three years, initially on anti-submarine duties, but later as surface search and torpedo-attack aircraft. The squadron went with "Ark Royal" to the Atlantic, and by April 1940 they were supporting Allied operations during the Norwegian campaign, where they bombed Vaernes airfield. After the withdrawal from Norway, "Ark Royal" and the squadron moved to the Mediterranean in June. Aircraft from 820 squadron were involved in attacking the French fleet at Mers-el-Kébir, and later the Battle of Dakar, as well as attacks at Cagliari. They were also active during the Battle of Cape Spartivento, as well as covering convoys to Malta.