The Saunders-Roe A27 London emanated from Air Ministry Specification R24/31 which called for an open sea patrol flying boat. The first prototype flew in March 1934 and went on to serve with Nos 209 and 210 Squadrons at RAF Felixtowe and Gibraltar respectively. Deliveries of production aircraft, the London MkI began two years later in March 1936, the receiving unit being No 201 Squadron at Calshot. Whilst the first machines were powered by 2 x Bristol Pegasus III 9-cylinder radial engines of 820 hp, the eleventh and subsequent aircraft were equipped with the more powerful Pegasus X and designated the London MkII. A first claim to fame was in 1937-38, when 5 aircraft of No 204 Squadron, configured with auxiliary fuel tanks, flew to Australia to mark the 150th anniversary of the founding of the Colony at Sidney.
The London carried a crew of 6 personnel and was armed with 3 x .303 Lewis machine guns; one mounted forward at the bow, one aft and the third amidships. Offensive ordnance comprised bombs, mines or depth charges of up to 2,000 lb in weight carried on the lower wing.
At the outbreak of the Second World War in 1939, Londons equipped No 201 squadron at Sullom Voe in the Shetlands, No 240 Squadron at Invergordon on the Cromarty Firth and No 202 Squadron at Gibraltar. The UK units conducted active maritime patrols over the North Sea to watch for enemy naval forces breaking out into the Atlantic and report the return to Germany of blockade runners, whilst No 202 Squadron carried out long distance patrols in the Western Mediterranean. All such duties were taken over by the Hudson and Sunderland during the first 6 months of 1940 and the London was retired in 1941.
The London equipped 7 RAF squadrons at one time or another and a few were transferred to the Royal Canadian Air Force in late 1940. A total of 31 aircraft were built and there are no known survivors.