 The aircraft were fitted with an additional fuel tank and armour, and the single French 7.5 mm Darne machine gun was replaced by four British machine guns.It was intended that they be used as anti-submarine patrol aircraft operating from the escort carrier , but it was soon realised that the Chesapeake lacked the power to fly from such a small vessel while carrying a useful load, and they were reassigned to training squadrons in November 1941, and the squadron received Swordfish Mk.2's as replacements.From August to December 1942 811 Squadron was based at RAF Bircham Newton in Norfolk, serving under the control of RAF Coastal Command, and flying on anti-shipping and mine-laying operations.