The Saro Lerwick flying boat was one of the least successful aircraft to serve with the RAF during the Second World War, and demonstrated the danger of ordering a new design off the drawing board.
The Lerwick was designed to satisfy Air Ministry specification R.1/36, for a twin engined general purpose flying boat to replace the Short Sunderland. The new aircraft was to have a cruising speed of 230mph, a range of 1,500 miles and to be able to carry 2,000lb of bombs. Supermarine, Shorts, Fairey, Blackburn and Saunder-Roe all put forwards proposals. Supermarine were eliminated because of the urgency of the Spitfire programme. Blackburn were awarded with a contract to produce a single example of their unique B-20 (the boat part of the hull could be lowered hydraulically to raise the engines above the water during landing and takeoff).
The original Saunders-Roe design was for an aircraft with a shallow hull and gull wings. This was then modified to one with a deep hull and flatter wings, and an order was placed for ten aircraft. No prototype was built.
The first Lerwick made its maiden flight in October 1938. It was an all-metal monoplane with cantilevered wings, powered by two 1,375hp Bristol Hercules HE.1M radial engines. The 2,000lb bomb load was carried within the engine nacelles. Defensive firepower was provided by a single Vickers K gun in a retractable FN.7 nose turret, a twin-Browning armed FN.8 dorsal turret and a four-gun FN.4A turret in the tail. During the design process the crew had risen from six to nine, and the aircraft was significantly heavier that specified.
Flight tests revealed the Lerwick to be a deeply flawed aircraft. It was unstable in every axis, making hands-off flight impossible. This immediately made it unsuited to its intended role as a long range patrol aircraft, making it far too tiring to fly for long periods. It was just as unstable in the water, and needed far too much space to take off.
Saunders-Roe made a series of attempts to rescue their design. One aircraft received two auxiliary fins and an extended chord rudder, but remained just as unstable. Eventually a much larger fin with larger rudder was installed, but even this only produced a minor improvement in performance. Four Lerwicks were delivered to No.240 Squadron to replace their Saro Londons during the summer of 1939, but in October the process was abandoned, and on 24 October the entire programme was suspended.
The failure of the Lerwick caused a desperate shortage of flying boats during 1940, for production of the Short Sunderland had been scaled down in the expectation that it was about to be replaced by the new aircraft. As a result the RAF was forced to attempt to use the Lerwick on active service. The programme was reactivated on 1 November 1939, and in December 1939 No.209 Squadron at Oban received its first aircraft.
Despite all of the efforts made to improve the Lerwick, it was a disastrous failure in service. The first aircraft was lost on 20 February 1940, after one of the wing-floats collapsed on landing. A second aircraft would be lost in the same way in June. During the summer of 1940 No.209 Squadron moved to Pembroke Dock, but any hope that it could contribute to the battle of the Atlantic ended when the Lerwick had to be grounded for more modifications. The squadron returned to Scotland in November. Two Lerwicks sank at their moorings before the end of the year, another was lost attempting to take off on 7 January 1941 and a fourth aircraft disappeared without trace on 22 February. By this point enough Catalinas were available for the Lerwicks to be moved to a training unit, where more aircraft were lost in accidents. After a brief return to service with No.422 Squadron (RCAF) in 1942, at the end of October 1942 the surviving Lerwicks were retired.