The de Havilland DH.91 Albatross was a four-engined British transport aircraft of the 1930s. A total of seven aircraft were built between 1938–39. Development The DH.91 was designed in 1936 by A. E. Hagg to Air Ministry specification 36/35 for a transatlantic mail plane. The aircraft was notable for the ply-balsa-ply sandwich construction of its fuselage, later used in the de Havilland Mosquito bomber. Another unique feature was a cooling system for the air-cooled engines that allowed nearly ideal streamlining of the engine mounting. The first Albatross flew on 20 May 1937. The second prototype broke in two during overload tests but was repaired with minor reinforcement. The first and second prototypes were operated by Imperial Airways. Although designed as a mailplane, a version to carry 22 passengers was developed; the main differences being extra windows and the replacement of split flaps with slotted flaps. Five examples formed the production order delivered in 1938/1939. When war was declared all seven aircraft were operating from Bristol/Whitchurch to Lisbon and Shannon. Operational history As normal for the Imperial Airways fleet of the time, all were given names starting with the same letter, and the first aircraft's name was also used as a generic description for the type overall, as "Frobisher Class". This tradition, which came from a maritime and railway background of classes of ships and locomotives, lasted well into postwar days with BOAC and BEA. The first delivery to Imperial Airways was the 22-passenger DH.91 Frobisher in October 1938. The five passenger-carrying aircraft were operated on routes from Croydon to Paris, Brussels and Zurich. After test flying was completed, the two prototypes were delivered to Imperial Airways as long-range mail carriers. The only significant season of their operation was the summer of 1939, when they were the main type on the two-hourly London Croydon-to-Paris Le Bourget passenger route. With the onset of World War II, the Royal Air Force considered their range and speed useful for courier flights between Great Britain and Iceland, and the two mail planes were pressed into service with 271 Squadron in September 1940, operating between Prestwick and Reykjavik, but both were destroyed in landing accidents in Reykjavík within the space of 9 months: Faraday in 1941 and Franklin in 1942. The five passenger aircraft were used by Imperial Airways, (BOAC from September 1940) on Bristol–Lisbon and Bristol–Shannon routes from Bristol (Whitchurch) Airport. Frobisher was destroyed during