Avro 549 Aldershot The Avro 549 Aldershot was a British single - engined bomber aircraft built by Avro . Development and design . The Aldershot was designed to meet the 1920 British Specification 2 / 20 for a long - range day and night bomber to be powered by a Rolls - Royce Condor engine . The specification required a range of 500 miles ( 800 km ) and a bombload of 2 , 000 lb ( 900 kg ) , originally comprising a single World War I vintage 1 , 800 lb ( 820 kg ) SN bomb , but then changed to four 500 lb ( 230 kg ) bombs carried externally or eight 250 lb ( 114 kg ) bombs internally . The Air Ministry gave Avro a contract for two prototypes , designated Aldershot I , on 2 December 1920 , in competition with the de Havilland Derby . The first prototype flew at Hamble Aerodrome near Southampton in October 1921 . As a result of test flying , the fuselage was lengthened by 6 ft ( 2 m ) in order to improve directional control , being displayed in this form at the RAF Display at Hendon on 24 June , the second prototype flying in July , with the lengthened fuselage and a modified undercarriage . The first prototype was modified as a testbed for the water - cooled Napier Cub engine , in this form becoming the Aldershot II , flying on 15 December 1922 . It was later used to test the slow - revving 850 hp ( 630 kW ) Beardmore Typhoon I inline engine , flying in this form on 10 January 1927 . The Aldershot was a three - bay biplane , with a steel framed fuselage structure with plywood and fabric covering , and wooden wings . The pilot and navigator were seated side - by side in a cockpit behind the upper wing trailing edge , with additional accommodation for the navigator , who was also the bomb - aimer in a cabin inside the fuselage , which was provided with four circular windows on each side . A gunner sat in a separate cockpit behind the pilot , and was armed with a Lewis gun on a Scarff ring . Another Lewis gun could be fitted to a ventral mounting in the cabin , while there was provision for a fixed , forward firing Vickers machine gun operated by the pilot , although this was rarely fitted . A bomb - bay forward of the cabin could hold eight 250 lb ( 114 kg ) bombs , with larger bombs being carried externally under the fuselage . The Aldershot also formed the basis for the Avro Andover transport , which used the same wings , tail and power plant but had a new fuselage . Operational history . When it was evaluated against the de Havilland Derby , the Aldershot proved to be the superior aircraft , with the mixed construction Aldershot being about 800 lb ( 360 kg ) lighter than the all - wooden Derby , which had no provision for carrying its bombload internally , or for any ventral armament . On 26 January 1923 , the Air Ministry ordered 15 aircraft under the designation Aldershot III . The only operator of the aircraft was No . 99 Squadron RAF which reformed on 1 April 1924 , receiving its Aldershots from July that year . The Aldershot was mainly used for night flying , but occasionally flew day bombing exercises . Unlike the other members of the RAF ' s heavy bomber force , it was operated in an all - silver colour scheme , rather than the dark - green NIVO scheme usually used for night operations . By 1925 , the Air Ministry had decided that heavy bombers should have multiple engines , and 99 Squadron started to receive the twin - engined Handley Page Hyderabad in January 1926 , with the Aldershots being completely replaced in Squadron service by March that year .