It then transferred its Seals to 822 Naval Air Squadron and received as replacements Blackburn Shark IIs, which it used to take up the role of Torpedo Spotter Reconnaissance.

By September 1937 the Sharks had been replaced by Fairey Swordfish and the Squadron transferred to the new aircraft carrier HMS Ark Royal in November 1938.

They carried out bombing raids on Rhodes, and in Egypt were active in supporting ground forces at Maaten Bagush, Gambut and Daba.

821 Squadron was transferred again in November 1942 to operate out of RAF Hal Far, on Malta, attacking enemy supply convoys headed to North Africa.

Four of the squadron's aircraft were transferred to Castel Benito, Tripoli in March 1943 to support night bombing raids by the Royal Air Force in Libya.