Sukhoi Su - 6 The Sukhoi Su - 6 was a Soviet ground attack aircraft developed during World War II . The mixed - power ( rocket and piston engines ) high - altitude interceptor Su - 7 was based on the single - seat Su - 6 prototype . Design and development . Development of the Su - 6 began in 1939 , when the Sukhoi design bureau began work on a single - seat armoured ground - attack aircraft . An order for two prototypes was placed on 4 March 1940 , and on 1 March 1941 flight testing of the first prototype was begun by test pilot A . I . Kokin . The flight tests indicated that the Su - 6 was superior to the Ilyushin Il - 2 in nearly all performance categories , however its engine exceeded its age limit before testing could be completed , and no further Shvetsov M - 71 engines were available . The second prototype flew only in January 1942 because the OKB had to be evacuated after the start of the Great Patriotic War . It was armed with two 23 mm cannon , four machine guns and ten rails for aerial rockets . Test results were very favorable , and the AFRA Scientific Research Institute recommended the acquisition of a small production batch for testing under front - line conditions . A draft resolution for the production of 25 aircraft was prepared , however unfortunately for Sukhoi , it was never officially issued . Meanwhile , combat experience with single - seat Il - 2s demonstrated the need for a rear gunner . The third prototype was therefore designed with the second crewman at the expense of bomb load ( decreased from 400 kg / 881 lb to 200 kg / 440 lb ) , and was fitted with a more powerful M - 71F engine . Official tests revealed that the two - seat Su - 6 had a 100 km / h ( 54 kn , 62 mph ) greater top speed than the Il - 2 , although with a considerably smaller payload . When the troublesome M - 71 was canceled , Sukhoi was directed to utilize the liquid - cooled Mikulin AM - 42 engine . When flight tests began on 22 February 1944 , the re - engined Su - 6 proved inferior to the Ilyushin Il - 10 using the same engine thanks to the additional 250 kg ( 551 lb ) of armor required to protect the liquid - cooled engine and the lower power output of the AM - 42 compared with M - 71F . Although Su - 6 never entered production , in 1943 Pavel Sukhoi was awarded the Stalin Prize of the 1st Degree for the development of the aircraft . Su - 7 . As an experiment , the basic single - seat Su - 6 design was converted into a mixed - power high - altitude interceptor named Su - 7 ( the name was reused in 1950s for a supersonic fighter - bomber ) . The armor was removed and the fuselage was of all - metal construction . Power came from a Shvetsov ASh - 82 FN piston engine with two TK - 3 turbochargers in the nose and a Glushko RD - 1 - KhZ rocket engine in the tail . The piston engine produced 1 , 380 kW ( 1 , 850 hp ) , while the rocket engine utilized kerosene and nitric acid for fuel and generated 2 . 9 kN ( 600 lbf ) of thrust for up to 4 minutes . Armament consisted of three 20 mm ShVAK cannon with 370 rounds of ammunition . The sole Su - 7 was completed in 1944 . Test flights demonstrated a top speed of 510 km / h ( 275 kn , 315 mph ) at 12 , 000 m ( 39 , 370 ft ) without the rocket motor , and 705 km / h ( 380 kn , 440 mph ) with the rocket . In 1945 , the rocket motor exploded during flight testing , killing the pilot and destroying the aircraft .