Hawker Hart The Hawker Hart was a British two - seater biplane light bomber aircraft of the Royal Air Force ( RAF ) . It was designed during the 1920s by Sydney Camm and manufactured by Hawker Aircraft . The Hart was a prominent British aircraft in the inter - war period , but was obsolete and already side - lined for newer monoplane aircraft designs by the start of the Second World War , playing only minor roles in the conflict before being retired . Several major variants of the Hart were developed , including a navalised version for the Royal Navy ' s aircraft carrier s . Beyond Britain , the Hart would be operated by a number of foreign nations , including Sweden , Yugoslavia , Estonia , South Africa , and Canada . Design and development . In 1926 , the Air Ministry stated a requirement for a two - seat high - performance light day - bomber , to be of all - metal construction and with a maximum speed of 160 mph ( 258 km / h ) . Designs were tendered by Hawker , Avro and de Havilland . Fairey , who had sold a squadron ' s worth of its wooden Fox bomber in 1925 , was not at first invited to tender to the specification , and was only sent a copy of the specification after protesting to the Chief of the Air Staff , Hugh Trenchard . Hawker ' s design was a single - bay biplane powered by a Rolls - Royce F . XI water - cooled V12 engine ( the engine that later became known as the Rolls - Royce Kestrel ) . It had , as the specification required , a metal structure , with a fuselage structure of steel - tube covered by aluminium panels and fabric , with the wings having steel spars and duralumin ribs , covered in fabric . The crew of two sat in individual tandem cockpits , with the pilot sitting under the wing trailing edge , and operating a single . 303 in ( 7 . 7 mm ) Vickers machine gun mounted on the port side of the cockpit . The observer sat behind the pilot , and was armed with a single Lewis gun on a ring mount , while for bomb - aiming , he lay prone under the pilots seat . Up to 520 pounds ( 240 kg ) of bombs could be carried under the aircraft ' s wings . " J9052 " , the prototype Hart , first flew in June 1928 , being delivered to the Aeroplane and Armament Experimental Establishment at RAF Martlesham Heath on 8 September . It demonstrated good performance and handling , reaching 176 mph ( 283 km / h ) in level flight and in a vertical dive . The competition culminated in the choice of the Hawker Hart in April 1929 . The de Havilland Hound was rejected due to handling problems during landing and because of its part - wooden primary structure . While the Avro Antelope demonstrated similar performance and good handling , the Hart was preferred as it was far cheaper to maintain , a vital aspect to a programme during defence budget constraints that the British armed forces faced during the 1920s . The Fairey Fox IIM ( which despite the name was effectively an all - new aircraft ) , delayed by Fairey ' s late start on the design compared to the other competitors , only flew for the first time on 25 October 1929 , long after the Hart had been selected . A total of 992 aircraft were built as Harts . It became the most widely used light bomber of its time and the design would prove to be a successful one with a number of derivatives , including the Hawker Hind and Hector , being made . There were a number of Hart variants made , though only slight alterations were made . The Hart India was a tropicalised version of the aircraft ; the Hart Special was a tropicalised Hawker Audax , a Hart variant , with desert equipment ; a specialised Hart Trainer was also built which dispensed with the gunners ring . Vickers built 114 of the latter model at Weybridge between 1931 and June 1936 . The production Hart day bomber had a single 525 hp ( 390 kW ) Rolls - Royce Kestrel IB 12 - cylinder V - type engine ; a speed of 184 mph ( 296 km / h ) and a range of 470 mi ( 757 km ) . It was faster than most contemporary fighters , an astonishing achievement considering it was a light bomber , and had high manoeuvrability , making the Hart one of the most effective biplane bombers ever produced for the Royal Air Force . In particular , it was faster than the Bristol Bulldog , which had recently entered service as the RAF ' s front line fighter . This disparity in performance led the RAF to gradually replace the Bulldog with the Hawker Fury . Demand was such that production was spread out among a wide selection of aircraft companies . Of the 962 built in the United Kingdom , Hawker produced 234 , Armstrong Whitworth 456 , Gloster 46 , Vickers 226 , and 42 were produced in Sweden under licence by ASJA who built 18 , Götaverken who built 3 , and the Central Workshops of the Air Force ( CVM ) who built 21 . 1004 Harts were produced . Operational history . The Hart entered service with No . 33 Squadron RAF in February 1930 , replacing the larger and slower Hawker Horsley . No . 12 Squadron replaced its Foxes with Harts in January 1931 , with a further two British - based Hart light bomber squadrons forming during 1931 . Harts were deployed to the Middle East during the Abyssinia Crisis of 1935 – 1936 . The Hart saw extensive and successful service on the North - West Frontier , British India during the inter - war period . Four Hawker Harts from the Swedish Air Force saw action as dive bombers during the 1939 – 1940 Winter War as part of a Swedish volunteer squadron , designated F19 , fighting on the Finnish side . Though obsolete compared to the United Kingdom ' s opposition at the start of the Second World War , the Hart continued in service , mainly performing in the communications and training roles until being declared obsolete in 1943 . The Hart proved to be a successful export , seeing service with the Royal Egyptian Air Force , Royal Indian Air Force , South African Air Force , Estonian Air Force , Southern Rhodesia , Sweden ( where it was designated B4 ) and Kingdom of Yugoslavia . Swedish Air Force General Björn Bjuggren wrote in his memoirs how his squadron developed dive - bombing techniques in the mid - 1930s for their B4s . When the Hawker engineers found out , they issued a formal objection , saying that the aircraft had not been designed for that purpose ; however , Swedish pilots proved that the aircraft was up to that task and dispelled their concern . Variants . Audax . The Hawker Audax was a Hart variant , designed for the army co - operation role , seeing much service in the British Empire . The first Audax flew in late 1931 , and eventually , over 700 Audaxes were produced ( including export ) . The Audax was very similar to the Hart , though had some modifications , including a hook to pick up messages . The Audax was armed with a single . 303 in ( 7 . 7 mm ) Lewis light machine gun and a . 303 in ( 7 . 7 mm ) Vickers machine gun . The Audax was powered by a version of the Kestrel engine and had a maximum speed of 170 mph ( 274 km / h ) . A number of variants of the Audax were produced , including the Audax India , a tropicalised version of the Audax for service in India ; the Audax Singapore for service there . The Audax saw service with other air forces , including the Royal Canadian Air Force , the Royal Indian Air Force , the South African Air Force , the Royal Egyptian Air Force , the Royal Iraqi Air Force , the Imperial Iranian Air Force , the Straits Settlements and the Southern Rhodesian Air Force . The Audax saw limited service during the Second World War , seeing service in Africa on the Kenya - Abyssinia border , the latter of which had been occupied by Italy . The Audax also saw service in Iraq , at RAF Habbaniya , west of Baghdad , after the uprising there , the Anglo - Iraqi War ; influenced by Axis forces . The battle for RAF Habbaniya : In the days leading up to the battle for RAF Habbaniya crews [ Squadron Leader Tony Dungeon for example ] began to upgrade the Audaxs stationed there , despite having received orders forbidding such actions . They fitted some of the Audaxs to carry 250 lb [ 113 kg ] bombs instead of 20 lb ( 9 kg ) bombs . The Audax ended its service by 1945 . A derivative of the Audax , the Hawker Hartebeest , a light bomber , was built for the South African Air Force with modifications made from the Audax . Sixty - five of these aircraft were built , the majority in South Africa . The aircraft saw action in East Africa during clashes against Italy who occupied Abyssinia . A . V . Roe and Co . built 287 Audaxes as part of the RAF expansion scheme during 1935 – 1937 . These did not warrant an Avro type number , but between 1937 and 1938 Avro built 24 modernised Audaxes for the Egyptian government , powered by 750 hp ( 560 kW ) Armstrong Siddeley Panther VIA radials . Acknowledging the amount of redesign work done , these were designated the Avro Type 674 . Demon . The Hawker Demon was a fighter variant of the Hart light bomber . It was developed as when the Hart entered service , it was virtually uninterceptable by the RAF ' s fighters , which was demonstrated in air defence exercises where they were sometimes instructed to restrict their height and speed in order to give the RAF ' s Siskin s and Bulldogs a chance . While the Hawker Fury offered better performance , it was expensive and was only available in small numbers , so when a fighter version of the Hart was suggested , the Air Ministry selected the type as an interim fighter until higher performance dedicated fighters could be bought in larger numbers . The new fighter variant added a second Vickers machine gun , while the coaming of the rear cockpit was angled to give a better field of fire , and a supercharged Kestrel IS engine was fitted . Evaluation of an initial batch of six aircraft , known as Hart Fighters by one flight of 23 Squadron during 1931 was successful , and larger orders followed for the fighter Hart , now known as the Hawker Demon . First Flight on February 10 , 1933 . 305 Hawker Demons were built including 232 for the RAF . The Demon were powered by varying types of the Kestrel engine . It had an armament of a single rear . 303 in ( 7 . 7 mm ) Lewis Gun with two . 303 in ( 7 . 7 mm ) Vickers machine guns in the nose . Large numbers of the type were fitted with a hydraulically powered turret in the rear , which had been tested on the Hawker Hart . The Demon was also sold to the Royal Australian Air Force . It saw only brief second line operations during the Second World War . Production of the Demon was by Hawker and by Boulton Paul Aircraft , Norwich . Hardy . The Hawker Hardy was a general - purpose variant of the " Hawker Hart " tropicalised to meet Air Ministry Specification G . 23 / 33 as a Wapiti replacement in Iraq . The prototype was a production Hart which was modified with a modified radiator , a message pick - up hook , water containers and a desert survival kit . The prototype first flew on 7 September 1934 , and the first production aircraft were delivered to 30 Squadron in January 1935 . The " Hardy " saw some service during the Second World War , in Africa and the Middle East ; the " Hardys " performing a number of operations against Italian - occupied Abyssinia as well as other areas of Africa . The " Hardy " also saw service with Southern Rhodesia . The last operational sortie by a Hardy was on 9 May 1941 and most of the survivors were scrapped , although some continued in service as communications aircraft . On 14 May 1941 , the Belgian Colonial authorities obtained a Hawker Hardy from the South African Air Force . Painted in Belgian colours , the machine was used for observation missions , but unfortunately overturned while landing at Gambela airfield on 26 May 1941 , effectively writing off the aircraft . Hind . The Hawker Hind was a derivative of the Hart and was intended to replace it . The Hawker Hector was a variant of the Hind and was used in the army co - operation role . It saw only limited service during the Second World War with the Royal Air Force . Hectors were also sold to Ireland . Osprey . The Hawker Osprey was the navalised carrier - borne version of the Hart , performing in the fighter and reconnaissance roles . The Osprey had a single Rolls - Royce Kestrel II engine , and had a max speed of 168 mph ( 270 km / h ) . Its armament consisted of a single forward . 303 in ( 7 . 7 mm ) Vickers machine gun and one . 303 in ( 7 . 7 mm ) Lewis gun . The Osprey joined the Fleet Air Arm ( FAA ) in 1932 , with 103 being built , and ended its career in 1944 after serving as a trainer for FAA pilots during her career in the Second World War . By December 1936 , Ospreys were being deployed by 701 Squadron based at RAF Kalafrana in the anti - submarine and anti - piracy role . The Osprey was also sold to the Swedish Air Force being used on the seaplane cruiser , which carried six Ospreys . Ospreys were also sold to the air forces of Portugal and the Spanish Republican Air Force .