The Lerwick was Saunders-Roe’s answer to Air Ministry Specification R1/36 calling for a medium range flying boat for anti-submarine, convoy escort and reconnaissance duties. A contract was let in June 1937 to purchase 21 aircraft and the first machine off the production line took to the air on 31 October 1938.
A twin-engined monoplane powered by 2 Bristol Hercules II radial engines, each of 1,375 hp, the Lerwick was of all-metal construction with a conventional flying boat hull and featured 2 stabilising floats on long struts mounted under the wings. Manned by a crew of 6, it was armed with a single .303 in Vickers K machine gun in a nose turret, 2 x .303 in Browning machine guns in the dorsal position and 4 x .303 in Brownings in a tail turret. Its weapon load comprised 2,000 lb of bombs or depth charges.
The Lerwick was unstable both in the air and on water and possessed a vicious stall; moreover, it could not maintain height on one engine, nor could the torque on a single engine at full power be contained. Numerous early modifications failed to correct its various handling problems. Nevertheless, the advent of war forced its entry into service in 1940 with No 209 Squadron based at Oban, soon after which aircraft began being lost in flying accidents – in several instances when wing floats broke away causing the machine to roll over and sink. On only 2 occasions were u-boats attacked and on neither was the submarine damaged.
In April 1941, No 209 Squadron began being re-equipped with the Catalina and Lerwicks were withdrawn from service the following month – coincidentally as the 21st and final aircraft rolled off the production line. In the summer of 1942, they returned to service for a short time as training machines with Nos 422 and 423 squadrons of the Royal Canadian Air Force operating from Lough Erne, but at the end of that year were declared obsolete and scrapped.