In 1938 , BB-1 was used as the plat form to start design of a ground-attac aircraft ( GAA ) , Compared to its prototype , it featured an M-88 engine , strengthened armour , modified landing gear design and a number of other differences . The GAA aeroplane ( BB-2 ) passed into testing in the summer of 1940 The cust omer having upgraded the attack aircraft requirements , in the summer of 1939 , the design bureau of P.0. Sukhoi started to develop a conceptual design of a single-seat armoured attack aircraft . In the aut umn , the SSAAA design was accepted and approved A 4th March 1940 resolution of USSR CPC Defence Committee P.O. Sukhoi was officially given the Job " To design and build a single-engine armoured single-seat attack aircraft with the M-71 enginei-the aircraft to be built in a set of two prototypes i Work on the first prototype began in mid-aprl1 1940 and dragged on till late January 1941 , which was due to the Design Bureau moving to a new location , the inadequate production infrastructure of plant No 289 and the unavailability of the M-71 engine On lst March 1941 pilot A , I . Kokin started an accelerated programme of manufacturers tests , which continued till late August . The tests established that in terms of flight speed , rate-of-climb and takeoff and landing performance , the M-71 Su-6 was vastly superior to the AM-38 Il-2 , but lack of cannon and missile armaments posed a serious obstacle to its production , Between 25th September and 10th October , the aeroplane underwent verification tests at the AFRA Scientific Research Inatitute . The tests were never completed in full as the only available M-71 engine reached its age limit The second Su-6 attack aircraft prototype under construction was completed in January 1942 . In contrast to the firat prototype , it featured two Vya-23 shkas cannons , four SHKAS machine-guns and ten RE for PS-82 or PS-132 The manufacturer's tests of the aeroplane were conducted between 15th