Blohm & Voss Ha 137 The Blohm & Voss Ha 137 was a German ground - attack aircraft of the 1930s . It was Blohm & Voss ' entry into the contest to equip the re - forming " Luftwaffe " with its first purpose - built dive bomber . Although the contest would eventually be won by the Junkers Ju 87 , the Ha 137 demonstrated that B & V ' s Hamburger Flugzeugbau , not even two years old at this point , had a truly capable design team of its own . It is of interest to note that one Ha 137 single - seat prototype competed against the Henschel Hs 123 at Rechlin . Design and development . Hamburger had already designed a biplane trainer of no particular distinction , the Ha 135 under its first designer , Reinhold Mewes . Mewes then left to join another small company , Fieseler . In his place , Hamburger hired Richard Vogt , who had been working for a decade with Kawasaki Aircraft and was looking to return to Germany . Before leaving Japan , Vogt had been working on a new design for building wing spars , using a single chrome - plated steel tube ( often square or rectangular ) that formed both the middle portion of the wing and also served as a primary fuel tank . When tenders were offered for the dive bomber program in 1934 , Hamburger was not even invited to submit an entry . Nevertheless , Vogt was convinced that his new construction method would deliver an aeroplane of the required strength with better performance than traditional designs , so he started work on Projekt " 6 and submitted it anyway . He also started work on a more conventional biplane design as Projekt " 7 . " Projekt " 6 was essentially a scaled - up version of Vogt ' s last design at Kawasaki , the Kawasaki Ki - 5 . Built entirely of metal and using a semi - monocoque fuselage , the design looked more like a fighter - specifically like the Heinkel He 112 - than a dive bomber . The wing used the tubular spar system , the inner portion of which was sealed as a fuel tank holding 270 L ( 70 US gal ) . The design used fixed landing gear , so in order to reduce their length , and thus the drag , the wings featured a sharp inverted gull wing bend at about ¼ span . The wheels were mounted on two shock absorber s each , so the fairing around the gear was large enough to allow the mounting of a 7 . 92 mm ( . 312 in ) MG 17 machine gun for testing , and a 20 mm MG FF cannon if required . Two additional 7 . 92 mm ( . 312 in ) MG 17s were mounted in the fuselage decking above the engine . Engines proved to be more of a problem . Vogt originally submitted the design mounting the new BMW XV . The future of this engine was in doubt , however , and the Reich Air Ministry ( RLM ) asked for the design to be re - submitted with the 485 kW ( 650 hp ) Pratt & Whitney Hornet radial engine , then starting licensed production in Germany as the BMW 132 . Vogt ' s team then modified the design to use the Hornet as Projekt " 6a , or alternately the Rolls - Royce Kestrel as Projekt " 6b . The RLM found the resulting design interesting enough to fund construction of three prototypes . The Hornet - powered Ha 137 V1 first flew in April 1935 , followed the next month by V2 , and both were shipped to Travemünde that summer . It quickly became apparent that the Hornet engine was so large that the visibility during diving was greatly affected , and the RLM then suggested that the third prototype be completed as a 6b with the Kestrel , delaying it slightly to change the engine mounts and add a somewhat odd - looking radiator under the nose . By this point the definitive requirements for the dive bomber program had been drawn up , taken directly from Junkers ' description of its own entry which had already been selected to win , calling for a two - seater arrangement . The Ha 137 was thus excluded , although realistically no other design had a chance to win anyway . The RLM was nevertheless interested enough in the design to order another three prototypes with the new Junkers Jumo 210 engine . The radial - powered versions retroactively became known as the Ha 137A , while the inline powered versions became the Ha 137B . Further testing continued during 1936 , and the prototypes also took part in the " doomed " dive bomber contest in June 1936 , but the design was still being considered for the close support role instead of dive bomber . However , when Ernst Udet took over the T - Amt later that year , he considered the close support role unnecessary , and informed Hamburger that it should stop work on the design . The three Jumo - powered prototypes were built anyway during 1936 and 1937 , eventually being used as testbed aircraft at Blohm & Voss . V1 was destroyed in testing during 1935 when the ammunition for its guns exploded , and V6 , " D - IDTE " , crashed in July 1937 , but the remaining four were used for years until a lack of spare parts for their engines eventually grounded them . Vogt had also done some work on a navalized version of the design as Projekt 11 ; however , the additional weight of the landing equipment , or floats as in the 11b , dramatically reduced range and made the design unfeasible .