It was intended to be used with the Short Sunderland in Royal Air Force Coastal Command but it was a flawed design and only a small number were built.

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 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.

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 aircraft was a compact twin-engined, high-winged monoplane of all-metal construction, with a conventional flying boat hull, a planing bottom and two stabilising floats, carried under the wings on long struts.

In December 1939, Air Vice-Marshal Sholto Douglas recommended that 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 the Second World War, aircraft were urgently required.

[12] 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[citation needed] Marine Aircraft Experimental Establishment at Helensburgh.

[13] Data from Saunders Roe and Saro Aircraft since 1917[14]General characteristics Performance Armament Eleven of the 21 Lerwicks built were lost or written off during the three years the type saw operational service.