Saro Lerwick The Saunders - Roe A . 36 Lerwick was a British flying boat built by Saunders - Roe Limited ( Saro ) . It was intended to serve alongside the Short Sunderland in the Royal Air Force ' s Coastal Command , but it was a flawed design and only a small number were built . They had a poor service record and a high accident rate - out of 21 aircraft , 10 were lost to accidents and one for an unknown reason . Design and development . Air Ministry Specification R . 1 / 36 ( to meet Operational Requirement 32 ) was issued in March 1936 to several companies that had experience in building flying boats . The specification was for a smaller flying boat for anti - submarine , convoy escort and reconnaissance duties . It would replace the Royal Air Force ' s biplane flying boats such as the Saro London and Supermarine Stranraer . The specification called for a cruise speed on 230 mph , and a weight of no more than 25 , 000 lb . Designs were tendered by Saunders - Roe ( S . 36 ) , Supermarine ( Type 314 ) , Blackburn Aircraft ( b . 20 ) and Shorts . The Blackburn B . 20 was a radical design that offered much better performance by reducing the drag associated with a flying boat hull and so a prototype was ordered to test the concept . Of the other designs the Supermarine was the first choice with Saro and Shorts tied in second place . The Supermarine was ordered " off the drawing board " i . e . without requiring prototypes to be produced and flown first . However Supermarine ' s commitment to the Spitfire meant that work was not expected to start for two years and so the Ministry looked to the other designs . Saunders - Roe had redesigned the S . 36 in the meantime – replacing low hull and gull wing with a deep body and high wing – and the Supermarine order was transferred to the S . 36 . The contract was issued in June 1937 to buy 21 of the S . 36 receiving the service name Lerwick ( after the coastal town of the same name ) . The Lerwick was a compact twin - engined , high - winged monoplane of all - metal construction . It had a conventional flying boat hull with a planing bottom and two stabilising floats carried under the wings on long struts . It was powered by two Bristol Hercules radial engines and initially had twin fins and rudders . For defence , the Lerwick was equipped with three powered gun turret s . The nose turret had a single 0 . 303 inch Vickers K gun ; the other two had 0 . 303 Browning machine guns , two guns in the Nash & Thomson FN . 8 turret in the dorsal position and four in the Nash & Thomson FN4 . A turret at the tail . Offensive weapons were a total of 2000 lb ( 900 kg ) of bombs or depth charges – four 500 lb or eight 250 lb bombs , or four depth charges – which were carried in two streamlined nacelles behind the engines ; a configuration shared by the Martin PBM Mariner . The first three aircraft were used as prototypes , with the first being launched on 31 October 1938 after numerous delays during design and construction . The Lerwick was immediately found to be unstable both aerodynamically and on the water , and not suited to " hands off " flying . The latter was a major problem in an aircraft designed for long - range patrols . Numerous adjustments , including the addition of a greatly enlarged single fin and an increase in the wing angle of incidence , failed to remedy its undesirable characteristics which included a vicious stall and unsatisfactory rates of roll and yaw . In service , several aircraft were lost because of wing floats breaking off , suggesting this was a structural weakness . Persistent problems with the aircraft ' s hydraulics resulted in bomb doors sometimes dropping open during flight On one engine the Lerwick could not maintain height , nor could it maintain a constant heading as the controls could not counter the torque of one engine on maximum power . Hence , an engine failure would inevitably see the aircraft flying in slowly descending circles . On one occasion , the loss of an engine forced a Lerwick to make an emergency landing in the Caledonian Canal . The aircraft was then towed to Oban at the end of a string of coal barges . Service . In the summer of 1939 , four Lerwicks were allocated to 240 Squadron . By October , the squadron had stopped flying them and reverted to its older and slower Saro London flying boats . The Lerwick programme was cancelled on the 24 October but restarted on 1 November . In December 1939 , Air Vice - Marshal Sholto Douglas recommended the Lerwicks be scrapped and Saunders - Roe put to building Short Sunderlands but the production change would have taken months and with the start of World War II , aircraft were urgently required . Production continued and the type entered service with 209 Squadron based at Oban in 1940 , replacing Short Singapores . The squadron soon began losing aircraft to accidents . During the service with 209 Squadron , all the Lerwicks were grounded twice for urgent safety modifications ; on only two occasions were U - boats ever attacked by a Lerwick and neither of the submarines was damaged . In April 1941 , 209 Squadron began receiving the US Consolidated Catalina . The last of a total of 21 Lerwicks was delivered in May but the type was withdrawn from front - line service in the same month . Most of the remaining Lerwicks were transferred to Number 4 ( Coastal ) Operational Training Unit at Invergordon ; three were sent to 240 Squadron for service trials at the highly - secret Marine Aircraft Experimental Establishment at Helensburgh . In the Summer of 1942 , the Lerwicks were briefly returned to service for the purpose of operational training with 422 Squadron and 423 Squadron of the Royal Canadian Air Force , based at Loch Erne . By the end of 1942 the type had been declared obsolete ; by early 1943 the survivors had been scrapped .